You have a pointer at index 0 in an array of size arrLen. At each step, you can move 1 position to the left, 1 position to the right in the array or stay in the same place  (The pointer should not be placed outside the array at any time).
Given two integers steps and arrLen, return the number of ways such that your pointer still at index 0 after exactly steps steps.
Since the answer may be too large, return it modulo 10^9 + 7.
 
Example 1:
Input: steps = 3, arrLen = 2
Output: 4
Explanation: There are 4 differents ways to stay at index 0 after 3 steps.
Right, Left, Stay
Stay, Right, Left
Right, Stay, Left
Stay, Stay, Stay

Example 2:
Input: steps = 2, arrLen = 4
Output: 2
Explanation: There are 2 differents ways to stay at index 0 after 2 steps
Right, Left
Stay, Stay

Example 3:
Input: steps = 4, arrLen = 2
Output: 8

 
Constraints:

1 <= steps <= 500
1 <= arrLen <= 10^6

Source: leetcode | Difficulty: MEDIUM
Tags: Dynamic programming

Starter code: class Solution:
    def numWays(self, steps: int, arrLen: int) -> int:
        

Solutions:
class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		r = min(arrLen, steps // 2 + 1)
		dp = [0, 1]
		for t in range(steps):
			dp[1:] = [sum(dp[i - 1:i + 2]) for i in range(1, min(r + 1, t + 3))]
		return dp[1] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		waysDict = {}
		return self.numWaysRec(steps, arrLen, 0, waysDict) % (10 ** 9 + 7)

	def numWaysRec(self, steps: int, arrLen: int, currentPos: int, waysDict: dict) -> int:
		if steps == currentPos or (steps == 1 and currentPos == 0):
			return 1
		totalWays = 0
		for nextMove in self.validMoves(steps, currentPos, arrLen):
			if (nextMove, steps - 1) in waysDict:
				totalWays += waysDict[nextMove, steps - 1]
			else:
				result = self.numWaysRec(steps - 1, arrLen, nextMove, waysDict)
				waysDict[nextMove, steps - 1] = result
				totalWays += result
		return totalWays

	def updateDict(self, steps: int, currentPos: int) -> None:
		pass

	def validMoves(self, steps: int, currentPos: int, arrLen: int) -> list:
		validList = []
		if currentPos - 1 <= steps - 1 and currentPos - 1 >= 0:
			validList.append(currentPos - 1)
		if currentPos <= steps - 1:
			validList.append(currentPos)
		if currentPos + 1 <= steps - 1 and currentPos + 1 < arrLen:
			validList.append(currentPos + 1)
		return validList

	def numWaysTree(self, steps: int, arrLen: int) -> int:
		pass

	def numWaysTreeRec(self, steps: int, arrLen: int, counter: list, currentPos: int) -> None:
		if steps == 1 and currentPos == 0 or steps == currentPos:
			counter[0] += 1


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if steps is None or steps < 0 or (not arrLen):
			return 0
		arrLen = min(arrLen, steps + 1)
		memo = [[0] * arrLen for _ in range(steps + 1)]
		memo[0][0] = 1
		for i in range(1, steps + 1):
			for j in range(arrLen):
				memo[i][j] += memo[i - 1][j]
				if j > 0:
					memo[i][j] += memo[i - 1][j - 1]
				if j < arrLen - 1:
					memo[i][j] += memo[i - 1][j + 1]
		return memo[steps][0] % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		moves = [-1, 0, 1]

		@lru_cache(maxsize=2048)
		def count(s, position=0):
			if position < 0 or position >= arrLen:
				return 0
			if s == 0:
				return 1 if position == 0 else 0
			number_of_moves = 0
			for delta in moves:
				new_position = position + delta
				number_of_moves += count(s - 1, new_position)
			return number_of_moves
		return count(steps) % (10 ** 9 + 7)


class Solution:

	def count_paths(self, i, s, n, memo):
		if i < 0 or i > min(n - 1, s):
			return 0
		if s == 0 and i == 0:
			return 1
		if (s, i) in memo:
			return memo[s, i]
		else:
			memo[s, i] = self.count_paths(i - 1, s - 1, n, memo) + self.count_paths(i, s - 1, n, memo) + self.count_paths(i + 1, s - 1, n, memo)
		return memo[s, i]

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = {}
		return self.count_paths(0, steps, arrLen, memo) % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		n = min(arrLen, steps)
		m = 10 ** 9 + 7
		dp = [[0 for i in range(n)] for i in range(steps + 1)]
		dp[0][0] = 1
		for i in range(1, steps + 1):
			for j in range(n):
				if j - 1 < 0:
					dp[i][j] = (dp[i - 1][j] + dp[i - 1][j + 1]) % m
				elif j + 1 >= n:
					dp[i][j] = (dp[i - 1][j] + dp[i - 1][j - 1]) % m
				else:
					dp[i][j] = (dp[i - 1][j] + dp[i - 1][j - 1] + dp[i - 1][j + 1]) % m
		return dp[steps][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(arrLen, steps)
		r = [[0] * arrLen for _ in range(steps)]
		r[0][0] = 1
		r[0][1] = 1
		mod = 10 ** 9 + 7
		for t in range(steps):
			for i in range(arrLen):
				r[t][i] += r[t - 1][i] + (r[t - 1][i - 1] if i > 0 else 0) + (r[t - 1][i + 1] if i < arrLen - 1 else 0)
				r[t][i] = r[t][i] % mod
		return r[t][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		kmod = pow(10, 9) + 7
		arrLen = min(steps, arrLen)
		dp = [[0] * arrLen for _ in range(steps + 1)]
		dp[0][0] = 1
		dirs = [0, -1, 1]
		for s in range(steps):
			for i in range(arrLen):
				if dp[s][i]:
					for d in dirs:
						j = i + d
						if j < 0 or j >= arrLen:
							continue
						dp[s + 1][j] += dp[s][i]
			for i in range(arrLen):
				dp[s + 1][i] %= kmod
		return dp[steps][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = {}
		for i in range(steps + 1):
			dp[i] = defaultdict(int)
		dp[1][1] += 1
		dp[1][0] += 1
		for i in range(2, steps + 1):
			for index in dp[i - 1].keys():
				if index + 1 < arrLen:
					dp[i][index + 1] += dp[i - 1][index]
				if index - 1 >= 0:
					dp[i][index - 1] += dp[i - 1][index]
				dp[i][index] += dp[i - 1][index]
		return dp[steps][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		right_most = min(steps + 1 // 2, arrLen)
		dp = [[0 for __ in range(right_most)] for _ in range(steps)]
		for i in range(steps):
			if i == 0:
				dp[0][0] = 1
				dp[0][1] = 1
			else:
				for j in range(right_most):
					dp[i][j] = dp[i - 1][j]
					if j > 0:
						dp[i][j] += dp[i - 1][j - 1]
					if j < right_most - 1:
						dp[i][j] += dp[i - 1][j + 1]
		return dp[-1][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(arrLen, steps // 2 + 1)
		dp = [0] * arrLen
		dp[0] = 1
		for i in range(steps):
			dp = [(dp[x - 1] if x >= 1 else 0) + dp[x] + (dp[x + 1] if x + 1 < arrLen else 0) for x in range(arrLen)]
		return dp[0] % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		MOD = 10 ** 9 + 7

		@lru_cache(maxsize=steps * arrLen)
		def num_ways(current, target, steps):
			if not 0 <= target < arrLen:
				return 0
			if steps == 0:
				return 1 if current == target else 0
			elif steps == 1:
				return 1 if abs(current - target) <= 1 else 0
			return (num_ways(current, target, steps - 1) + num_ways(current, target - 1, steps - 1) + num_ways(current, target + 1, steps - 1)) % MOD
		return num_ways(0, 0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		n = min(steps, arrLen)
		dp = [0] * n
		dp[0] = 1
		for step in range(1, steps + 1):
			tmp_dp = [0] * n
			for idx in range(n):
				tmp_dp[idx] = sum(dp[max(0, idx - 1):min(idx + 1, n) + 1])
			dp = tmp_dp
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.memo = {}

		def dfs(steps, pos):
			if pos < 0 or pos >= arrLen or pos > steps:
				return 0
			if steps == 0:
				if pos == 0:
					return 1
				return 0
			if self.memo.get((steps, pos), None) is not None:
				return self.memo.get((steps, pos))
			ret = dfs(steps - 1, pos - 1)
			ret = ret % (10 ** 9 + 7)
			ret += dfs(steps - 1, pos)
			ret = ret % (10 ** 9 + 7)
			ret += dfs(steps - 1, pos + 1)
			ret = ret % (10 ** 9 + 7)
			self.memo.update({(steps, pos): ret})
			return ret
		return dfs(steps, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = [[0] * min(steps + 1, arrLen) for _ in range(steps + 1)]
		dp[0][0] = 1
		(m, n) = (len(dp), len(dp[0]))
		for step in range(1, steps + 1):
			for pos in range(n):
				dp[step][pos] += dp[step - 1][pos]
				if pos - 1 >= 0:
					dp[step][pos] += dp[step - 1][pos - 1]
				if pos + 1 < n:
					dp[step][pos] += dp[step - 1][pos + 1]
		return dp[-1][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		ways = [[0] * min(251, arrLen) for _ in range(steps + 1)]
		ways[0][0] = 1
		for k in range(1, steps + 1):
			for i in range(len(ways[k])):
				for offset in [-1, 0, 1]:
					if 0 <= i + offset < len(ways[k]):
						ways[k][i] += ways[k - 1][i + offset]
				ways[k][i] %= 10 ** 9 + 7
		return ways[-1][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		M = 10 ** 9 + 7

		@lru_cache(None)
		def help(s, i):
			if s == 1:
				return 1 if i <= min(1, arrLen - 1) else 0
			out = help(s - 1, i)
			if i > 0:
				out += help(s - 1, i - 1)
			if i < arrLen - 1:
				out += help(s - 1, i + 1)
			return out % M
		return help(steps, 0)


import math

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.cache = {}
		self.array_length = arrLen - 1
		return self._numWays(0, steps) % (10 ** 9 + 7)

	def _numWays(self, position, steps):
		if position > steps:
			return 0
		if (position, steps) in self.cache:
			return self.cache[position, steps]
		if steps == 1:
			if position in (-1, 0, 1):
				return 1
			else:
				return 0
		options = 0
		if position > 0:
			options += self._numWays(position - 1, steps - 1)
		if position < self.array_length:
			options += self._numWays(position + 1, steps - 1)
		options += self._numWays(position, steps - 1)
		self.cache[position, steps] = options
		return options


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(arrLen, steps // 2 + 1)
		dp = [0] * arrLen
		dp[0] = 1
		for i in range(steps):
			dp = [(j - 1 >= 0 and dp[j - 1] or 0) + dp[j] + (j + 1 < arrLen and dp[j + 1] or 0) for j in range(arrLen)]
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		maxPos = min(steps, arrLen)
		mod = 10 ** 9 + 7
		f = [[0] * maxPos for _ in range(steps + 1)]
		f[1][0] = 1
		f[1][1] = 1
		for i in range(2, steps + 1):
			for j in range(maxPos):
				f[i][j] = f[i - 1][j]
				if j > 0:
					f[i][j] = (f[i][j] + f[i - 1][j - 1]) % mod
				if j < maxPos - 1:
					f[i][j] = (f[i][j] + f[i - 1][j + 1]) % mod
		return f[steps][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.steps = steps
		self.arrLen = arrLen
		self.memo = {}
		return self.dfs(steps, 0)

	def dfs(self, n, pos):
		if n == pos:
			return 1
		if n < pos or pos > self.arrLen - 1:
			return 0
		if (n, pos) in self.memo:
			return self.memo[n, pos]
		ans = 0
		if pos > 0:
			ans += self.dfs(n - 1, pos - 1)
		ans += self.dfs(n - 1, pos)
		if pos != self.arrLen - 1:
			ans += self.dfs(n - 1, pos + 1)
		ans %= 10 ** 9 + 7
		self.memo[n, pos] = ans
		return ans


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(None)
		def dp(index, steps):
			if index < 0 or index == arrLen:
				return 0
			if steps == 0:
				return 1 if index == 0 else 0
			ans = 0
			for i in range(-1, 2, 1):
				ans += dp(index + i, steps - 1)
				ans %= 10 ** 9 + 7
			return ans
		return dp(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.dp = collections.defaultdict(int)
		return self.helper(0, steps, arrLen)

	def helper(self, cur, steps, n):
		x = pow(10, 9) + 7
		if cur == 0 and steps == 0:
			return 1
		if abs(cur) > steps or cur < 0 or cur >= n:
			return 0
		if (cur, steps) in self.dp:
			return self.dp[cur, steps]
		res = self.helper(cur, steps - 1, n) + self.helper(cur - 1, steps - 1, n) + self.helper(cur + 1, steps - 1, n)
		self.dp[cur, steps] = res % x
		return res % x


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		ans = 0
		mem = [dict() for _ in range(501)]

		def dfs(s, arrLen, pos):
			nonlocal ans
			if pos < 0 or pos >= arrLen:
				return 0
			if s == 0 and pos == 0:
				return 1
			if s < 0:
				return 0
			if pos in mem[s]:
				return mem[s][pos]
			s1 = dfs(s - 1, arrLen, pos)
			s2 = dfs(s - 1, arrLen, pos + 1)
			s3 = dfs(s - 1, arrLen, pos - 1)
			total = s1 + s2 + s3
			if not pos in mem[s]:
				mem[s][pos] = total
			return total
		ans = dfs(steps, arrLen, 0)
		return ans % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		def ncr(n, r, p):
			num = den = 1
			for i in range(r):
				num = num * (n - i) % p
				den = den * (i + 1) % p
			return num * pow(den, p - 2, p) % p
		ans = 0
		dp = [[0 for i in range(min(steps, arrLen))] for j in range(steps + 1)]
		dp[1][1] = 1
		for k in range(2, steps + 1):
			for l in range(len(dp[k])):
				(f, b) = (l - 1, l + 1)
				if f >= 0 and f < len(dp[k]):
					dp[k][f] += dp[k - 1][l]
				if b >= 0 and b < len(dp[k]):
					dp[k][b] += dp[k - 1][l]
		for numstay in range(0, steps + 1):
			numMoves = steps - numstay
			if numMoves % 2 != 0:
				continue
			ans += ncr(numstay + numMoves, numstay, 1000000007) * dp[numMoves][0] % 1000000007
			ans = ans % 1000000007
		return ans + 1


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		nw = [[0 for _ in range(min(arrLen, steps + 1))] for _ in range(steps + 1)]
		nw[0][0] = 1
		for s in range(1, steps + 1):
			for idx in range(min(arrLen, steps + 1)):
				ways = nw[s - 1][idx]
				if idx > 0:
					ways += nw[s - 1][idx - 1]
				if idx < min(arrLen, steps + 1) - 1:
					ways += nw[s - 1][idx + 1]
				nw[s][idx] = ways
		return nw[steps][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		cases = {}

		def dfs(steps, pos):
			if (steps, pos) in cases:
				return cases[steps, pos]
			if steps == 0:
				return 1 if pos == 0 else 0
			if pos >= arrLen or pos < 0:
				return 0
			subcount = dfs(steps - 1, pos + 1) + dfs(steps - 1, pos) + dfs(steps - 1, pos - 1)
			cases[steps, pos] = subcount
			return subcount % (10 ** 9 + 7)
		return dfs(steps, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(None)
		def simulate(currIdx, stepsTaken):
			nonlocal arrLen
			nonlocal steps
			if stepsTaken == steps:
				if currIdx == 0:
					return 1
				return 0
			ret = 0
			moves = [currIdx, currIdx - 1, currIdx + 1]
			for nextIdx in moves:
				if nextIdx >= 0 and nextIdx < arrLen:
					ret += simulate(nextIdx, stepsTaken + 1)
			return ret
		return simulate(0, 0) % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = collections.defaultdict(int)

		def dfs(index, curr):
			if curr == steps:
				if index == 0:
					return 1
				else:
					return 0
			key = (index, curr)
			if key in memo:
				return memo[key]
			res = 0
			if index > 0:
				res += dfs(index - 1, curr + 1)
			if index < arrLen - 1:
				res += dfs(index + 1, curr + 1)
			res += dfs(index, curr + 1)
			memo[key] = res
			return res
		return dfs(0, 0) % (10 ** 9 + 7)


class Solution:

	def __init__(self):
		self.mnem = {}

	def numWays(self, steps: int, arrLen: int) -> int:

		def dp(pos, steps):
			if (pos, steps) in self.mnem:
				return self.mnem[pos, steps]
			if steps == 0:
				return 1 if pos == 0 else 0
			if pos < 0:
				return 0
			if pos >= arrLen:
				return 0
			result = dp(pos + 1, steps - 1) + dp(pos - 1, steps - 1) + dp(pos, steps - 1)
			self.mnem[pos, steps] = result
			return result
		return dp(0, steps) % (10 ** 9 + 7)


class Solution:

	def __init__(self):
		self.dp = {}

	def numWays(self, steps: int, arrLen: int, ptr: int=0) -> int:
		return self.numWays_dp(steps, min(arrLen, steps + 1), ptr) % (10 ** 9 + 7)

	def numWays_dp(self, steps: int, arrLen: int, ptr: int=0) -> int:
		if ptr >= arrLen:
			return 0
		if ptr < 0:
			return 0
		if steps == 0:
			if ptr == 0:
				return 1
			else:
				return 0
		if (ptr, steps) in self.dp:
			return self.dp[ptr, steps]
		left_ways = self.numWays(steps - 1, arrLen, ptr - 1)
		middle_ways = self.numWays(steps - 1, arrLen, ptr)
		right_ways = self.numWays(steps - 1, arrLen, ptr + 1)
		total_ways = left_ways + middle_ways + right_ways
		self.dp[ptr, steps] = total_ways
		return total_ways


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if arrLen == 1:
			return 1
		memo = {}
		return self.dfs(steps, arrLen, 0, memo)

	def dfs(self, steps, arrLen, currpos, memo):
		if (steps, currpos) in memo:
			return memo[steps, currpos]
		if currpos < 0 or currpos >= arrLen:
			return 0
		if steps == 0:
			if currpos == 0:
				return 1
			else:
				return 0
		memo[steps, currpos] = self.dfs(steps - 1, arrLen, currpos, memo) + self.dfs(steps - 1, arrLen, currpos + 1, memo) + self.dfs(steps - 1, arrLen, currpos - 1, memo)
		return memo[steps, currpos] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		visited = dict()

		def move(cur_index, cur_step):
			if (cur_index, cur_step) in visited:
				return visited[cur_index, cur_step]
			if cur_index < 0 or cur_index >= arrLen:
				visited[cur_index, cur_step] = 0
				return 0
			if cur_step == steps:
				if cur_index == 0:
					return 1
				return 0
			visited[cur_index, cur_step] = move(cur_index + 1, cur_step + 1) + move(cur_index - 1, cur_step + 1) + move(cur_index, cur_step + 1)
			return visited[cur_index, cur_step]
		move(0, 0)
		return move(0, 0) % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		MOD = 10 ** 9 + 7

		def dp(x, s, memo):
			if s == 0:
				if x == 0:
					return 1
				else:
					return 0
			if (x, s) not in memo:
				if x == 0:
					memo[x, s] = (dp(x + 1, s - 1, memo) + dp(x, s - 1, memo)) % MOD
				elif x == arrLen - 1:
					memo[x, s] = (dp(x - 1, s - 1, memo) + dp(x, s - 1, memo)) % MOD
				else:
					memo[x, s] = (dp(x + 1, s - 1, memo) + dp(x - 1, s - 1, memo) + dp(x, s - 1, memo)) % MOD
			return memo[x, s]
		return dp(0, steps, {})


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = {}

		def dfs(steps, ind):
			if (steps, ind) in dp:
				return dp[steps, ind]
			if steps == ind:
				return 1
			elif steps == 0:
				return 0
			res = 0
			res += dfs(steps - 1, ind)
			if ind > 0:
				res += dfs(steps - 1, ind - 1)
			if ind < arrLen - 1:
				res += dfs(steps - 1, ind + 1)
			dp[steps, ind] = res
			return res % (10 ** 9 + 7)
		return dfs(steps, 0)


def memoize(f):
	d = {}

	def memoized_f(*args):
		if args not in d:
			d[args] = f(*args)
		return d[args]
	return memoized_f

@memoize
def numWaysHelper(steps, arrLen, position):
	if position < 0 or position >= arrLen:
		return 0
	if steps == 0:
		if position == 0:
			return 1
		return 0
	big_num = 10 ** 9 + 7
	return (numWaysHelper(steps - 1, arrLen, position - 1) + numWaysHelper(steps - 1, arrLen, position) + numWaysHelper(steps - 1, arrLen, position + 1)) % big_num

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		return numWaysHelper(steps, arrLen, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mod = 10 ** 9 + 7
		memo = {}

		def dfs(steps, i):
			if not steps:
				return int(i == 0)
			if (steps, i) in memo:
				return memo[steps, i]
			res = dfs(steps - 1, i)
			if i - 1 >= 0:
				res += dfs(steps - 1, i - 1)
			if i + 1 <= arrLen - 1:
				res += dfs(steps - 1, i + 1)
			memo[steps, i] = res % mod
			return memo[steps, i]
		return dfs(steps, 0)


class Solution:

	def numWays(self, s: int, a: int) -> int:
		MOD = 1000000007
		mem = {}

		def f(s, a, i):
			if (s, i) in mem:
				return mem[s, i]
			if not s:
				if i:
					return 0
				return 1
			if i < 0 or i == a:
				return 0
			ans = 0
			ans += f(s - 1, a, i)
			ans += f(s - 1, a, i - 1)
			ans += f(s - 1, a, i + 1)
			mem[s, i] = ans
			return ans % MOD
		return f(s, a, 0)


MOD = int(1000000000.0 + 7)

class Solution:

	def get_count(self, counts, i):
		if i < 0 or i >= len(counts):
			return 0
		else:
			return counts[i]

	def numWays(self, steps: int, arrLen: int) -> int:
		counts = [1]
		for si in range(1, steps + 1):
			new_len = min(si + 1, arrLen)
			new_counts = [0] * new_len
			for i in range(new_len):
				new_counts[i] = sum((self.get_count(counts, j) for j in range(i - 1, i + 1 + 1))) % MOD
			counts = new_counts
		return counts[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		return self.getWays(0, steps, 0, arrLen, {})

	def getWays(self, step, steps, position, arrLen, cache):
		if step == steps:
			return position == 0
		if (step, position) in cache:
			return cache[step, position]
		numWays = 0
		if position > 0:
			numWays += self.getWays(step + 1, steps, position - 1, arrLen, cache)
		if position < arrLen - 1:
			numWays += self.getWays(step + 1, steps, position + 1, arrLen, cache)
		numWays += self.getWays(step + 1, steps, position, arrLen, cache)
		cache[step, position] = numWays
		return numWays % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = {}

		def helper(position, num_steps, idx):
			nonlocal steps, arrLen, memo
			if (position, num_steps, idx) in memo:
				return memo[position, num_steps, idx]
			if idx < 0 or idx > arrLen - 1:
				return 0
			if num_steps == steps:
				if position == 0:
					return 1
				return 0
			stay = helper(position, num_steps + 1, idx)
			right = helper(position + 1, num_steps + 1, idx + 1)
			left = helper(position - 1, num_steps + 1, idx - 1)
			memo[position, num_steps, idx] = stay + left + right
			return memo[position, num_steps, idx]
		return helper(0, 0, 0) % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		states = [{0: 1}, {}]
		base = 0
		mod = 1000000007
		shift = [1, 0, -1]
		for k in range(0, steps):
			nxt = (base + 1) % 2
			states[nxt].clear()
			for p in states[base].keys():
				for j in range(0, 3):
					np = p + shift[j]
					if 0 <= np < arrLen:
						if np not in states[nxt].keys():
							states[nxt][np] = 0
						states[nxt][np] = (states[nxt][np] + states[base][p]) % mod
			base = nxt
		return states[base][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mod = 10 ** 9 + 7
		n = arrLen
		A = [0, 1]
		for t in range(steps):
			A[1:] = [sum(A[i - 1:i + 2]) % mod for i in range(1, min(n + 1, t + 3))]
		return A[1] % mod


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if steps is None or steps < 0 or (not arrLen):
			return 0
		memo = {}
		return self.dfs(steps, arrLen, 0, memo)

	def dfs(self, steps, arrLen, pos, memo):
		if (steps, pos) in memo:
			return memo[steps, pos]
		if pos < 0 or pos > arrLen - 1:
			memo[steps, pos] = 0
			return 0
		if steps == 0:
			return 1 if pos == 0 else 0
		memo[steps, pos] = self.dfs(steps - 1, arrLen, pos - 1, memo) + self.dfs(steps - 1, arrLen, pos, memo) + self.dfs(steps - 1, arrLen, pos + 1, memo)
		return memo[steps, pos] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mod = 10 ** 9 + 7
		real_len = min(steps, arrLen) + 2
		f1 = [0 for _ in range(real_len)]
		f1[0] = 1
		for _ in range(steps):
			f2 = [0 for _ in range(real_len)]
			for i in range(real_len - 1):
				for d in [-1, 0, 1]:
					ii = i + d
					if ii >= 0 and ii <= arrLen - 1:
						f2[i] += f1[ii] % mod
			f1 = f2.copy()
		return f1[0] % mod


from functools import lru_cache

class Solution:

	@lru_cache(None)
	def helper(self, index, n, arrlen):
		if not 0 <= index < arrlen or n < 0 or index > n:
			return 0
		if index == n:
			return 1
		return (self.helper(index + 1, n - 1, arrlen) + self.helper(index - 1, n - 1, arrlen) + self.helper(index, n - 1, arrlen)) % self.MOD

	def numWays(self, steps: int, arrLen: int) -> int:
		self.MOD = 10 ** 9 + 7
		return self.helper(0, steps, arrLen)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		def count(pos, i):
			if i == steps:
				return pos == 0
			if (pos, i) in memo:
				return memo[pos, i]
			res = 0
			if pos > 0:
				res += count(pos - 1, i + 1)
				res %= mod
			if pos < arrLen - 1:
				res += count(pos + 1, i + 1)
				res %= mod
			res %= mod
			res += count(pos, i + 1)
			res %= mod
			memo[pos, i] = res
			return res
		mod = 10 ** 9 + 7
		memo = {}
		return count(0, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		MOD = 10 ** 9 + 7
		memo = {}

		def nw(i: int, k: int) -> int:
			if k == 0:
				return i == 0
			if k < 0 or i < 0 or i >= arrLen:
				return 0
			if (i, k) not in memo:
				memo[i, k] = (nw(i - 1, k - 1) + nw(i + 1, k - 1) + nw(i, k - 1)) % MOD
			return memo[i, k]
		return nw(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(steps // 2 + 1, arrLen)
		ans = [0] * arrLen
		ans[0] = 1
		for i in range(steps):
			new_ans = []
			for j in range(arrLen):
				tmp = ans[j]
				if j > 0:
					tmp += ans[j - 1]
				if j < arrLen - 1:
					tmp += ans[j + 1]
				new_ans.append(tmp)
			ans = new_ans
		return ans[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = dict()

		def calculateWays(steps, arrLen, index):
			if index < 0 or index >= arrLen:
				return 0
			elif steps == 0 and index == 0:
				return 1
			elif steps == 0 and index != 0:
				return 0
			elif (steps, index) in memo:
				return memo[steps, index]
			else:
				goLeft = calculateWays(steps - 1, arrLen, index - 1)
				stay = calculateWays(steps - 1, arrLen, index)
				goRight = calculateWays(steps - 1, arrLen, index + 1)
				memo[steps, index] = goLeft + stay + goRight
				return memo[steps, index]
		return calculateWays(steps, arrLen, 0) % (10 ** 9 + 7)


MODULO = 10 ** 9 + 7

class DP:

	def __init__(self, arrLen: int):
		self._len = arrLen
		self._cache = {}

	def get(self, index, steps):
		if (index, steps) in self._cache:
			return self._cache[index, steps]
		result = self._get_uncached(index, steps)
		self._cache[index, steps] = result
		return result

	def _get_uncached(self, index, steps):
		if index < 0 or index >= self._len:
			return 0
		if steps == 0 and index == 0:
			return 1
		elif steps == 0:
			return 0
		return (self.get(index - 1, steps - 1) + self.get(index, steps - 1) + self.get(index + 1, steps - 1)) % MODULO

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = DP(arrLen)
		return dp.get(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.arrLen = arrLen
		self.memo = {}
		return self.helper(steps, 0)

	def helper(self, steps, pos):
		if (steps, pos) in self.memo:
			return self.memo[steps, pos]
		if pos < 0 or pos >= self.arrLen or steps < 0:
			return 0
		if steps == 0:
			if pos == 0:
				return 1
			else:
				return 0
		res = 0
		for x in [-1, 0, 1]:
			ans = self.helper(steps - 1, pos + x)
			res += ans
		self.memo[steps, pos] = res % (10 ** 9 + 7)
		return res % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if arrLen == 0 or (arrLen == 1 and steps > 0):
			return arrLen
		combos = {}

		def _dfs_ways(steps, arrLen, loc=0, tar=0):
			if steps == 0:
				return 1 if loc == tar else 0
			if (steps, loc) in combos:
				return combos[steps, loc]
			steps -= 1
			(stay, right, left) = (0, 0, 0)
			stay = _dfs_ways(steps, arrLen, loc)
			if loc + 1 < arrLen:
				right = _dfs_ways(steps, arrLen, loc + 1)
			if loc - 1 >= 0:
				left = _dfs_ways(steps, arrLen, loc - 1)
			steps += 1
			res = (stay + left + right) % (math.pow(10, 9) + 7)
			combos[steps, loc] = res
			return res
		_dfs_ways(steps, arrLen)
		ans = combos[steps, 0]
		return int(ans % (math.pow(10, 9) + 7))


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.arrLen = arrLen

		@lru_cache(None)
		def dp(curr, steps):
			if steps:
				temp = 0
				for i in [curr - 1, curr, curr + 1]:
					if 0 <= i < self.arrLen:
						temp += dp(i, steps - 1)
				return temp
			else:
				return 1 if curr == 0 else 0
		return dp(0, steps) % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	@lru_cache(None)
	def recursive(self, x, i):
		if x == i:
			return 1
		count = 0
		if x > 0:
			count += self.recursive(x - 1, i)
			if i - 1 >= 0:
				count += self.recursive(x - 1, i - 1)
			if i + 1 < self.L:
				count += self.recursive(x - 1, i + 1)
		return count % (10 ** 9 + 7)

	def numWays(self, steps: int, arrLen: int) -> int:
		self.L = arrLen
		return self.recursive(steps, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.mod = 10 ** 9 + 7
		return self.dp(arrLen, steps, 0)

	@lru_cache(None)
	def dp(self, n, steps, i):
		if i >= n or i < 0:
			return 0
		if steps == 0:
			return 1 if i == 0 else 0
		stay_in_place = self.dp(n, steps - 1, i)
		move_left = self.dp(n, steps - 1, i - 1)
		move_right = self.dp(n, steps - 1, i + 1)
		return (stay_in_place + move_left + move_right) % self.mod


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		f_old = [0] * min(steps + 1, arrLen)
		f_new = [0] * min(steps + 1, arrLen)
		if arrLen == 1:
			return 1
		elif arrLen == 0:
			return 0
		f_old[0] = 1
		for i in range(steps):
			f_new[0] = f_old[0] + f_old[1]
			if i + 1 <= arrLen - 1:
				f_new[i + 1] = 1
			else:
				f_new[-1] = f_old[-1] + f_old[-2]
			for j in range(1, min(i + 1, arrLen - 1)):
				f_new[j] = f_old[j - 1] + f_old[j] + f_old[j + 1]
			f_old = f_new.copy()
			f_old = [_ % (10 ** 9 + 7) for _ in f_old]
		return f_old[0]


def count(curr, maxpos, steps, mod, obj):
	if curr < 0:
		return 0
	if curr == maxpos:
		return 0
	if steps == 1 and curr == 1:
		return 1
	if steps == 1 and curr == 0:
		return 1
	if steps == 0:
		return 0
	if (curr, steps) in obj:
		return obj[curr, steps]
	obj[curr, steps] = (count(curr, maxpos, steps - 1, mod, obj) % mod + count(curr + 1, maxpos, steps - 1, mod, obj) % mod + count(curr - 1, maxpos, steps - 1, mod, obj) % mod) % mod
	return obj[curr, steps]

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		curr = 0
		mod = 10 ** 9 + 7
		obj = {}
		return count(curr, arrLen, steps, mod, obj)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mem = {}

		def helper(i, k, arrLen):
			if i == 0 and k == 0:
				return 1
			if (i, k) in mem:
				return mem[i, k]
			count = 0
			for x in [-1, 0, 1]:
				if i + x < 0 or i + x >= arrLen or k < 0:
					continue
				count += helper(i + x, k - 1, arrLen)
			mem[i, k] = count
			return count
		return helper(0, steps, arrLen) % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mod = 10 ** 9 + 7

		@lru_cache(None)
		def dfs(s, l):
			if s == steps:
				if l == 0:
					return 1
				return 0
			return (dfs(s + 1, l) + (dfs(s + 1, l + 1) if l < arrLen - 1 else 0) + (dfs(s + 1, l - 1) if l else 0)) % mod
		return dfs(0, 0)


class Solution:

	def helper(self, pos, steps):
		if (pos, steps) in self.cache:
			return self.cache[pos, steps]
		if steps == 0:
			return 1 if pos == 0 else 0
		stay = self.helper(pos, steps - 1)
		self.cache[pos, steps - 1] = stay
		left = self.helper(pos + 1, steps - 1) if pos < self.arrLen - 1 else 0
		self.cache[pos + 1, steps - 1] = left
		right = self.helper(pos - 1, steps - 1) if pos > 0 else 0
		self.cache[pos - 1, steps - 1] = right
		return stay + left + right

	def numWays(self, steps: int, arrLen: int) -> int:
		self.cache = {}
		self.steps = steps
		self.arrLen = arrLen
		return self.helper(0, steps) % (10 ** 9 + 7)


import functools

@functools.lru_cache(maxsize=10 ** 7 + 1)
def count(curr, maxpos, steps, mod):
	if curr < 0:
		return 0
	if curr == maxpos:
		return 0
	if steps == 1 and curr == 1:
		return 1
	if steps == 1 and curr == 0:
		return 1
	if steps == 0:
		return 0
	return (count(curr, maxpos, steps - 1, mod) % mod + count(curr + 1, maxpos, steps - 1, mod) % mod + count(curr - 1, maxpos, steps - 1, mod) % mod) % mod

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		curr = 0
		mod = 10 ** 9 + 7
		return count(curr, arrLen, steps, mod)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		return self.dfs(steps, arrLen, {}, 0) % (10 ** 9 + 7)

	def dfs(self, step, arrLen, mem, index):
		if (step, index) in mem:
			return mem[step, index]
		if index < 0 or index >= arrLen:
			return 0
		if step == 0:
			if index == 0:
				return 1
			return 0
		mem[step, index] = 0
		for i in range(-1, 2):
			mem[step, index] += self.dfs(step - 1, arrLen, mem, index + i)
		return mem[step, index]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = [0 for _ in range(arrLen)]
		(dp[0], dp[1]) = (1, 1)
		for s in range(2, steps + 1):
			dp2 = [0 for _ in range(min(steps - s + 2, arrLen))]
			dp2[0] = dp[0] + dp[1]
			if arrLen != 1:
				dp2[-1] = dp[-2] + dp[-1]
			for num in range(1, min(steps - s + 1, arrLen - 1)):
				dp2[num] = dp[num - 1] + dp[num] + dp[num + 1]
			dp = dp2
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		c_ori = [0] * min(steps + 2, 2 + arrLen)
		c_ori[1] = 1
		c_new = [0] * min(steps + 2, 2 + arrLen)
		for i in range(0, steps):
			for j in range(1, len(c_ori) - 1):
				c_new[j] = c_ori[j] + c_ori[j - 1] + c_ori[j + 1]
			c_ori = c_new.copy()
		return c_ori[1] % 1000000007


LIMIT = 10 ** 9 + 7

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		max_pos = min(steps // 2 + 1, arrLen) + 1
		dp = [[0] * max_pos for _ in range(steps)]
		dp[0][0] = dp[0][1] = 1
		for i in range(1, steps):
			for j in range(max_pos - 1):
				dp[i][j] = (dp[i - 1][j] + dp[i - 1][j - 1] + dp[i - 1][j + 1]) % LIMIT
		return dp[-1][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		counts = [0] * min(arrLen, steps // 2 + 1)
		(counts[0], counts[1]) = (1, 1)
		mod = 10 ** 9 + 7
		while steps - 1:
			prev_counts = counts[:]
			for i in range(len(counts)):
				if i == 0:
					counts[i] = sum(prev_counts[i:i + 2]) % mod
				elif i == arrLen - 1:
					counts[i] = sum(prev_counts[i - 1:i + 1]) % mod
				else:
					counts[i] = sum(prev_counts[i - 1:i + 2]) % mod
			steps -= 1
		return counts[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if arrLen < 2:
			return 1
		MAX = 10 ** 9 + 7
		dp = [0] * arrLen
		dp[0] = 1
		dp[1] = 1
		ndp = [0] * arrLen
		for step in range(2, steps + 1):
			ndp[0] = dp[0] + dp[1]
			ndp[arrLen - 1] = dp[arrLen - 1] + dp[arrLen - 2]
			for i in range(1, min(steps, arrLen - 1)):
				ndp[i] = (dp[i - 1] + dp[i] + dp[i + 1]) % MAX
			dp[:min(steps, arrLen)] = ndp[:min(steps, arrLen)]
		return dp[0] % MAX


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		A = [0] * (arrLen + 2)
		A[1] = 1
		mod = 10 ** 9 + 7
		for n in range(1, steps + 1):
			prev = 0
			for m in range(1, min(arrLen + 1, n + 2)):
				old = A[m]
				A[m] = (prev + A[m] + A[m + 1]) % mod
				prev = old
		return A[1]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = [[0] * (steps // 2 + 2) for _ in range(steps + 1)]
		dp[0][0] = 1
		M = 10 ** 9 + 7
		for k in range(1, steps + 1):
			for i in range(steps // 2 + 1):
				if i == 0:
					dp[k][i] = (dp[k - 1][i] + dp[k - 1][i + 1]) % M
				elif i == arrLen - 1:
					dp[k][i] = (dp[k - 1][i] + dp[k - 1][i - 1]) % M
				else:
					dp[k][i] = (dp[k - 1][i] + dp[k - 1][i - 1] + dp[k - 1][i + 1]) % M
		return dp[steps][0] % M


from functools import lru_cache
mod = 10 ** 9 + 7

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(None)
		def calculation(pos: int, steps: int):
			if pos < 0 or pos >= arrLen:
				return 0
			if pos > steps:
				return 0
			if pos == steps:
				return 1
			return (calculation(pos + 1, steps - 1) + calculation(pos - 1, steps - 1) + calculation(pos, steps - 1)) % mod
		return calculation(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if steps == 0:
			return 0
		if arrLen == 1:
			return 1
		start = [1, 1] + [0] * (min(steps, arrLen) - 2)
		return self.numWaysHelper(steps - 1, start)

	def numWaysHelper(self, steps, start):
		if steps == 0:
			return start[0] % (10 ** 9 + 7)
		n = [0] * len(start)
		n[0] = start[0] + start[1]
		n[len(start) - 1] = start[len(start) - 1] + start[len(start) - 2]
		for i in range(1, len(start) - 1):
			n[i] = start[i - 1] + start[i] + start[i + 1]
		return self.numWaysHelper(steps - 1, n)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		max_len = min(steps // 2 + 1, arrLen)
		mod = 10 ** 9 + 7
		dp = [[0] * (max_len + 1) for _ in range(steps + 1)]
		dp[1][0] = 1
		dp[1][1] = 1
		for i in range(2, steps + 1):
			for j in range(max_len):
				dp[i][j] = (dp[i - 1][j] + dp[i - 1][j + 1] + (dp[i - 1][j - 1] if j > 0 else 0)) % mod
		for r in dp:
			print(r)
		return dp[steps][0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = [[0 for _ in range(min(steps + 1, arrLen))] for _ in range(steps + 1)]
		dp[0][0] = 1
		for s in range(1, steps + 1):
			for i in range(min(s + 1, arrLen, steps - s + 1)):
				dp[s][i] = dp[s - 1][i] % (10 ** 9 + 7)
				if i > 0:
					dp[s][i] += dp[s - 1][i - 1]
				if i < arrLen - 1:
					dp[s][i] += dp[s - 1][i + 1]
		return dp[-1][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		needed = min(steps + 1, arrLen)
		dp = [0 for i in range(needed + 1)]
		new_dp = dp.copy()
		dp[0] = 1
		for step in range(1, steps + 1):
			for pos in range(min(step + 1, arrLen)):
				new_dp[pos] = dp[pos] + dp[pos - 1] + dp[pos + 1]
			(dp, new_dp) = (new_dp, dp)
		return dp[0] % (10 ** 9 + 7)
		needed = min(arrLen, steps + 1)
		dp = [0 for i in range(needed + 1)]
		dp[0] = 1
		next_dp = dp.copy()
		for step in range(1, steps + 1):
			for pos in range(min(step + 1, arrLen)):
				next_dp[pos] = dp[pos - 1] + dp[pos] + dp[pos + 1]
			print((step, next_dp, dp))
			(dp, next_dp) = (next_dp, dp)
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		n = min(steps + 1, arrLen)
		dp = [0] * n
		dp[0] = 1
		MOD = 10 ** 9 + 7
		for _ in range(steps):
			ndp = [0] * n
			for i in range(n):
				if i == 0:
					ndp[i] = (dp[i] + dp[i + 1]) % MOD
				elif i == n - 1:
					ndp[i] = (dp[i - 1] + dp[i]) % MOD
				else:
					ndp[i] = (dp[i - 1] + dp[i] + dp[i + 1]) % MOD
			dp = ndp
		return dp[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		v = min(steps, arrLen)
		dp = [0] * v
		dp[0] = 1
		temp = [0] * v
		for _ in range(steps):
			left = 0
			for (idx, val) in enumerate(dp):
				temp = val
				right = 0 if idx == len(dp) - 1 else dp[idx + 1]
				dp[idx] += left + right
				left = temp
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(None)
		def helper(i, steps):
			if steps == 0:
				return i == 0
			elif steps < i or steps + i < 0:
				return 0
			else:
				result = helper(i, steps - 1)
				if i < arrLen - 1:
					result += helper(i + 1, steps - 1)
				if i > 0:
					result += helper(i - 1, steps - 1)
				return result % 1000000007
		mod = 1000000007
		return helper(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(arrLen, steps + 1)
		f = [1] + [0] * (arrLen - 1)
		for i in range(1, steps + 1):
			old = 0
			for j in range(arrLen):
				old_left = old
				old = f[j]
				if j > 0:
					f[j] += old_left
				if j < arrLen - 1:
					f[j] += f[j + 1]
		return f[0] % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	def numWays(self, steps, arrLen):
		arrLen = min(arrLen, steps + 1)
		f = [1] + [0] * (arrLen - 1)
		for i in range(1, steps + 1):
			old = 0
			for j in range(arrLen):
				old_left = old
				old = f[j]
				if j > 0:
					f[j] += old_left
				if j < arrLen - 1:
					f[j] += f[j + 1]
		return f[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		n = min(steps // 2 + 1, arrLen)
		f = [None] * (steps + 1)
		f[0] = [0] * n
		f[0][0] = 1
		for t in range(1, steps + 1):
			f[t] = [0] * n
			for i in range(n):
				f[t][i] = f[t - 1][i]
				if i + 1 < n:
					f[t][i] += f[t - 1][i + 1]
				if i - 1 >= 0:
					f[t][i] += f[t - 1][i - 1]
		return f[steps][0] % (10 ** 9 + 7)
		memo = {}

		def f(i, c):
			if c == 0:
				return 1 if i == 0 else 0
			if (i, c) in memo:
				return memo[i, c]
			cnt = f(i, c - 1)
			if i + 1 < arrLen:
				cnt += f(i + 1, c - 1)
			if i - 1 >= 0:
				cnt += f(i - 1, c - 1)
			memo[i, c] = cnt
			return cnt
		return f(0, steps) % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		modulo = 10 ** 9 + 7

		@lru_cache(None)
		def make_step(pos, steps_left):
			if steps_left == 0 or pos > steps_left:
				if pos == 0:
					return 1
				return 0
			else:
				ways = 0
				if pos > 0:
					ways += make_step(pos - 1, steps_left - 1) % modulo
				if pos < arrLen - 1:
					ways += make_step(pos + 1, steps_left - 1) % modulo
				ways += make_step(pos, steps_left - 1) % modulo
				return ways % modulo
		return make_step(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if arrLen > steps // 2 + 1:
			arrLen = steps // 2 + 1
		num_ways = [0 for i in range(arrLen)]
		num_ways[0] = 1
		k = 10 ** 9 + 7
		for _ in range(steps):
			cur_num_ways = num_ways[:]
			for i in range(arrLen):
				if i - 1 >= 0:
					cur_num_ways[i] += num_ways[i - 1]
				if i + 1 < arrLen:
					cur_num_ways[i] += num_ways[i + 1]
				cur_num_ways[i] = cur_num_ways[i] % k
			num_ways = cur_num_ways
		return num_ways[0]


from collections import defaultdict

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.counter = 0
		cache = defaultdict(defaultdict)

		def rec(pos, steps):
			if pos in cache:
				if steps in cache[pos]:
					return cache[pos][steps]
			if steps == 0:
				if pos == 0:
					return 1
				return
			if pos < 0 or pos >= arrLen:
				return
			if steps < pos:
				return
			left = rec(pos - 1, steps - 1)
			right = rec(pos + 1, steps - 1)
			stay = rec(pos, steps - 1)
			if left is None and right is None and (stay is None):
				val = None
			else:
				val = (left or 0) + (right or 0) + (stay or 0)
			cache[pos][steps] = val
			return val
		res = rec(0, steps)
		return res % (10 ** 9 + 7)


from functools import lru_cache

class Solution:

	def numWays(self, steps: int, n: int) -> int:
		MOD = 10 ** 9 + 7

		def calculate(pos, steps):
			nonlocal dp
			if pos < 0 or pos >= n:
				return 0
			if pos > steps:
				return 0
			if steps == pos:
				return 1
			steps -= 1
			if (pos + 1, steps) in dp:
				step1 = dp[pos + 1, steps]
			else:
				step1 = calculate(pos + 1, steps)
				dp[pos + 1, steps] = step1
			if (pos - 1, steps) in dp:
				step2 = dp[pos - 1, steps]
			else:
				step2 = calculate(pos - 1, steps)
				dp[pos - 1, steps] = step2
			if (pos, steps) in dp:
				step3 = dp[pos, steps]
			else:
				step3 = calculate(pos, steps)
				dp[pos, steps] = step3
			return (step1 + step2 + step3) % MOD
		dp = {}
		return calculate(0, steps)


class Solution:

	def numWays(self, steps: int, n: int) -> int:
		MOD = 10 ** 9 + 7

		@lru_cache(None)
		def calculate(pos, steps):
			if pos < 0 or pos >= n:
				return 0
			if pos > steps:
				return 0
			if steps == pos:
				return 1
			steps -= 1
			return (calculate(pos + 1, steps) + calculate(pos - 1, steps) + calculate(pos, steps)) % MOD
		return calculate(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		rec = [1]
		mod = 10 ** 9 + 7
		for i in range(1, steps + 1):
			temp = []
			for j in range(min(i + 1, arrLen)):
				temp.append(sum(rec[max(0, j - 1):min(j + 2, arrLen)]) % mod)
			rec = temp
		return rec[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if arrLen == 0 or arrLen == 1:
			return 1
		MODULO = 10 ** 9 + 7
		ans = [0] * arrLen
		ans[0] = 1
		ans[1] = 1
		arrLen = min(steps + 1, arrLen)
		for _ in range(1, steps):
			next_ans = [0] * arrLen
			for j in range(arrLen):
				if j == 0:
					next_ans[j] = (ans[j] + ans[j + 1]) % MODULO
				elif j == arrLen - 1:
					next_ans[j] = (ans[j - 1] + ans[j]) % MODULO
				else:
					next_ans[j] = (ans[j - 1] + ans[j] + ans[j + 1]) % MODULO
			ans = next_ans
		return ans[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		MOD = 10 ** 9 + 7

		def count_steps(steps_left, current_pos, memo):
			if (steps_left, current_pos) in memo:
				return memo[steps_left, current_pos]
			if current_pos < 0 or current_pos > arrLen - 1 or current_pos > steps_left:
				return 0
			if not steps_left:
				if current_pos == 0:
					return 1
				else:
					return 0
			ans = count_steps(steps_left - 1, current_pos, memo) + count_steps(steps_left - 1, current_pos - 1, memo) + count_steps(steps_left - 1, current_pos + 1, memo)
			memo[steps_left, current_pos] = ans % MOD
			return memo[steps_left, current_pos]
		return count_steps(steps, 0, {})


class Solution:
	dp = {}

	def traverse(self, pos, steps, arrLen):
		key = (pos, steps)
		dp = self.dp
		if key not in dp:
			if pos < 0 or pos >= arrLen:
				r = 0
			elif pos > steps:
				r = 0
			elif steps == 0:
				if pos == 0:
					r = 1
				else:
					r = 0
			else:
				r = (self.traverse(pos - 1, steps - 1, arrLen) + self.traverse(pos, steps - 1, arrLen) + self.traverse(pos + 1, steps - 1, arrLen)) % 1000000007
			dp[key] = r
		return dp[key]

	def numWays(self, steps: int, arrLen: int) -> int:
		self.dp = {}
		return self.traverse(0, steps, arrLen)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		kmod = pow(10, 9) + 7
		arrLen = min(steps, arrLen)
		dp = [0] * arrLen
		dp[0] = 1
		for s in range(steps):
			tmp = [0] * arrLen
			for i in range(arrLen):
				tmp[i] = dp[i]
				if i > 0:
					tmp[i] += dp[i - 1]
				if i < arrLen - 1:
					tmp[i] += dp[i + 1]
				tmp[i] %= kmod
			dp = list(tmp)
		return dp[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = {(0, 0): 1}
		N = 10 ** 9 + 7

		def dfs(x, t):
			if (x, t) not in memo:
				if x < 0 or x >= arrLen:
					res = 0
				elif x > t or x > steps - t:
					res = 0
				else:
					res = dfs(x + 1, t - 1) + dfs(x, t - 1) + dfs(x - 1, t - 1)
				memo[x, t] = res % N
			return memo[x, t]
		return dfs(0, steps)


class Solution:

	def numWays(self, steps: int, arrlen: int) -> int:
		mod = 10 ** 9 + 7
		if arrlen == 1:
			return 1
		dp = [[0] * min(arrlen, steps + 1) for _ in range(steps + 1)]
		dp[1][0] = 1
		dp[1][1] = 1
		for a in range(2, steps + 1):
			dp[a][0] = (dp[a - 1][0] + dp[a - 1][1]) % mod
			for b in range(1, min(arrlen, a + 1)):
				if b == arrlen - 1 or b == a:
					dp[a][b] = (dp[a - 1][b] + dp[a - 1][b - 1]) % mod
				else:
					dp[a][b] = (dp[a - 1][b] + dp[a - 1][b + 1] + dp[a - 1][b - 1]) % mod
		return dp[-1][0]


from functools import lru_cache

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(maxsize=None)
		def cc(step, pos):
			if step == steps:
				return 1 if pos == 1 else 0
			elif pos == 1:
				return cc(step + 1, pos + 1) + cc(step + 1, pos)
			elif pos == arrLen:
				return cc(step + 1, pos - 1) + cc(step + 1, pos)
			else:
				return cc(step + 1, pos + 1) + cc(step + 1, pos - 1) + cc(step + 1, pos)
		mod = int(10 ** 9 + 7)
		return cc(0, 1) % mod


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		if not arrLen or not steps:
			return 1
		if arrLen == 1:
			return 1
		shorter = min(steps, arrLen)
		dp = [[0 for _ in range(shorter)] for _ in range(steps + 1)]
		dp[0][0] = 1
		dp[1][0] = 1
		for i in range(1, steps + 1):
			for j in range(shorter):
				if j == 0:
					dp[i][j] = dp[i - 1][j] + dp[i - 1][j + 1]
				elif j == shorter - 1:
					dp[i][j] = dp[i - 1][j] + dp[i - 1][j - 1]
				else:
					dp[i][j] = dp[i - 1][j] + dp[i - 1][j + 1] + dp[i - 1][j - 1]
		return dp[-1][0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = {}
		MOD = 10 ** 9 + 7

		def moveOnce(i0, steps0):
			if steps0 == 0:
				if i0 == 0:
					return 1
				return 0
			if (i0, steps0) in dp:
				return dp[i0, steps0]
			if i0 > steps0:
				ans = 0
			elif i0 == 0:
				ans = moveOnce(i0 + 1, steps0 - 1) + moveOnce(i0, steps0 - 1)
			elif i0 == arrLen - 1:
				ans = moveOnce(i0 - 1, steps0 - 1) + moveOnce(i0, steps0 - 1)
			else:
				ans = moveOnce(i0 + 1, steps0 - 1) + moveOnce(i0 - 1, steps0 - 1) + moveOnce(i0, steps0 - 1)
			dp[i0, steps0] = ans % MOD
			return dp[i0, steps0]
		return moveOnce(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		self.dic = dict()
		self.search(steps, arrLen, 0)
		return self.search(steps, arrLen, 0) % (10 ** 9 + 7)

	def search(self, steps, arrLen, start):
		if (steps, start) in self.dic:
			return self.dic[steps, start]
		if start > steps:
			return 0
		if start == 0 and steps == 0:
			return 1
		output = 0
		output += self.search(steps - 1, arrLen, start)
		if start > 0:
			output += self.search(steps - 1, arrLen, start - 1)
		if start < arrLen - 1:
			output += self.search(steps - 1, arrLen, start + 1)
		self.dic[steps, start] = output
		return output


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		arrLen = min(steps + 1, arrLen)
		num = [0 for i in range(arrLen)]
		num[0] = 1
		modulo = 10 ** 9 + 7
		for i in range(steps):
			newnum = [num[i] for i in range(arrLen)]
			for i in range(arrLen):
				if i > 0:
					newnum[i] += num[i - 1]
				if i < arrLen - 1:
					newnum[i] += num[i + 1]
				if newnum[i] > modulo:
					newnum[i] %= modulo
			num = newnum
		return num[0]


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		MOD = 10 ** 9 + 7
		memory = {}

		def helper(i, steps):
			if i < 0 or i == arrLen:
				return 0
			if i > steps:
				return 0
			if i == steps:
				return 1
			prev = memory.get((i, steps))
			if prev is not None:
				return prev
			stay = helper(i, steps - 1)
			left = helper(i - 1, steps - 1)
			right = helper(i + 1, steps - 1)
			result = (stay + left + right) % MOD
			memory[i, steps] = result
			return result
		return helper(0, steps)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		mod = 10 ** 9 + 7

		@lru_cache(None)
		def dp(index, steps):
			if index < 0 or index >= arrLen:
				return 0
			if steps == 0:
				if index == 0:
					return 1
				return 0
			return (dp(index - 1, steps - 1) + dp(index + 1, steps - 1) + dp(index, steps - 1)) % mod
		return dp(0, steps) % mod


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:

		@lru_cache(None)
		def nw(pos, left):
			if pos < 0:
				return 0
			if pos >= arrLen:
				return 0
			if left == 0 and pos == 0:
				return 1
			if left == 0 and pos != 0:
				return 0
			res = nw(pos + 1, left - 1)
			res += nw(pos - 1, left - 1)
			res += nw(pos, left - 1)
			return res
		res = nw(0, steps)
		return res % 1000000007


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		maxPos = min(steps, arrLen)
		mod = 10 ** 9 + 7
		dp = [[0] * (maxPos + 1) for _ in range(steps + 1)]
		dp[1][0] = 1
		dp[1][1] = 1
		for s in range(2, steps + 1):
			for p in range(maxPos):
				dp[s][p] = dp[s - 1][p] + dp[s - 1][p + 1]
				dp[s][p] += dp[s - 1][p - 1] if p > 0 else 0
				dp[s][p] %= mod
		return dp[steps][0]


from collections import defaultdict

def numWays(steps: int, arrLen: int) -> int:
	if steps is None or steps < 0 or (not arrLen):
		return 0
	arrLen = min(arrLen, steps + 1)
	f = [[0] * arrLen for _ in range(steps + 1)]
	f[0][0] = 1
	for i in range(1, steps + 1):
		for j in range(min(arrLen, i + 1)):
			f[i][j] += f[i - 1][j]
			if j > 0:
				f[i][j] += f[i - 1][j - 1]
			if j < arrLen - 1:
				f[i][j] += f[i - 1][j + 1]
	return f[steps][0] % (10 ** 9 + 7)

class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		return numWays(steps, arrLen)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = {}
		const = 10 ** 9 + 7

		def num(step, idx) -> int:
			if (step, idx) in memo:
				return memo[step, idx]
			if idx < 0 or idx >= arrLen:
				return 0
			if step <= 0:
				return idx == step
			if idx > step:
				return 0
			elif idx == step:
				return 1
			else:
				memo[step, idx] = num(step - 1, idx) + num(step - 1, idx - 1) + num(step - 1, idx + 1)
				if memo[step, idx] > const:
					memo[step, idx] = memo[step, idx] % const
				return memo[step, idx]
		return num(steps, 0)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		memo = {}
		mod = 10 ** 9 + 7
		return self.dfs(steps, arrLen, 0, memo, mod)

	def dfs(self, steps, arrLen, pos, memo, mod):
		if (steps, pos) in memo:
			return memo[steps, pos]
		if steps == 0:
			if pos == 0:
				memo[steps, pos] = 1
				return 1
			return 0
		tmp = 0
		for d in (-1, 0, 1):
			nxt = pos + d
			if not 0 <= nxt < arrLen or nxt > steps:
				continue
			tmp += self.dfs(steps - 1, arrLen, nxt, memo, mod) % mod
		tmp %= mod
		memo[steps, pos] = tmp
		return tmp


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		l = min(steps, arrLen)
		dp = [0] * l
		dp[0] = 1
		for i in range(steps):
			nextdp = [0] * l
			for j in range(l):
				if j - 1 >= 0:
					nextdp[j] += dp[j - 1]
				nextdp[j] += dp[j]
				if j + 1 < l:
					nextdp[j] += dp[j + 1]
				nextdp[j] %= 10 ** 9 + 7
			dp = nextdp
		return dp[0] % (10 ** 9 + 7)


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		waysDict = {}
		return self.numWaysRec(steps, arrLen, 0, waysDict) % (10 ** 9 + 7)

	def numWaysRec(self, steps: int, arrLen: int, currentPos: int, waysDict: dict) -> int:
		if steps == currentPos or (steps == 1 and currentPos == 0):
			return 1
		totalWays = 0
		for nextMove in self.validMoves(steps, currentPos, arrLen):
			if (nextMove, steps - 1) in waysDict:
				totalWays += waysDict[nextMove, steps - 1]
			else:
				result = self.numWaysRec(steps - 1, arrLen, nextMove, waysDict)
				waysDict[nextMove, steps - 1] = result
				totalWays += result
		return totalWays

	def validMoves(self, steps: int, currentPos: int, arrLen: int) -> list:
		validList = []
		if currentPos - 1 <= steps - 1 and currentPos - 1 >= 0:
			validList.append(currentPos - 1)
		if currentPos <= steps - 1:
			validList.append(currentPos)
		if currentPos + 1 <= steps - 1 and currentPos + 1 < arrLen:
			validList.append(currentPos + 1)
		return validList


class Solution:

	def numWays(self, steps: int, arrLen: int) -> int:
		dp = [defaultdict(int) for _ in range(steps + 1)]
		dp[0][0] += 1
		dp[1][1] += 1
		dp[1][0] += 1
		modulo = pow(10, 9) + 7
		for i in range(2, steps + 1):
			for j in dp[i - 1].keys():
				remain = j - (steps - i)
				if j < 0:
					break
				if j + 1 < arrLen:
					dp[i][j + 1] += dp[i - 1][j]
				if j - 1 >= 0:
					dp[i][j - 1] += dp[i - 1][j]
				dp[i][j] += dp[i - 1][j]
		return dp[steps][0] % modulo