Given an array A of integers, return true if and only if it is a valid mountain array.
Recall that A is a mountain array if and only if:

A.length >= 3
There exists some i with 0 < i < A.length - 1 such that:
        
A[0] < A[1] < ... A[i-1] < A[i] 
A[i] > A[i+1] > ... > A[A.length - 1]





 
Example 1:
Input: [2,1]
Output: false


Example 2:
Input: [3,5,5]
Output: false


Example 3:
Input: [0,3,2,1]
Output: true


 
Note:

0 <= A.length <= 10000
0 <= A[i] <= 10000

Difficulty: EASY
Tags: Data structures
Skill types: Data structures

Starter code:
class Solution:
    def validMountainArray(self, A: List[int]) -> bool:
        

Solutions:
class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) <= 2:
			return False
		else:
			if A[1] < A[0]:
				return False
			is_up = True
			curr = A[0]
			for n in A[1:]:
				if n == curr:
					return False
				if n < curr:
					is_up = False
					curr = n
				if n > curr:
					if is_up:
						curr = n
					else:
						return False
			return not is_up


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		isIncreasing = True
		i = 1
		n = len(A)
		if n < 3:
			return False
		if A[1] <= A[0]:
			return False
		while i < n:
			if isIncreasing and A[i - 1] < A[i]:
				i += 1
				continue
			elif A[i] < A[i - 1]:
				isIncreasing = False
				i += 1
				continue
			else:
				return False
		if A[-1] >= A[-2]:
			return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		arr = A
		if len(arr) < 3:
			return False
		if arr[0] > arr[1]:
			return False
		if arr[-1] > arr[-2]:
			return False
		peek = None
		for i in range(1, len(arr) - 1):
			if arr[i] > arr[i + 1]:
				peek = i
			if peek and arr[i] < arr[i + 1]:
				return False
			if arr[i] == arr[i + 1] or arr[i] == arr[i - 1]:
				return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		dec = 0
		n = len(A)
		if n < 3:
			return False
		else:
			for i in range(n):
				if i != 0 and A[i] == A[i - 1]:
					return False
				elif i == 0 and A[i] > A[i + 1]:
					return False
				elif dec == 1 and A[i] > A[i - 1]:
					return False
				elif i != 0 and dec == 0 and (A[i] < A[i - 1]):
					dec = 1
				elif i == n - 1 and dec == 0:
					return False
			return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		N = len(A)
		if N < 3:
			return False
		i = 0
		while i < N - 1:
			if A[i] < A[i + 1]:
				i += 1
				print(i)
			else:
				break
		if i == 0 or i == N - 1:
			print('***')
			return False
		while i < N - 1:
			if A[i] > A[i + 1]:
				i += 1
				print(i)
			else:
				break
		if i == N - 1:
			return True
		else:
			print('1111')
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		length = len(A)
		if length < 3:
			return False
		prev = A[0]
		peak = -1
		for i in range(1, length):
			print(A[i])
			if A[i] > prev:
				if peak != -1:
					return False
			elif A[i] == prev:
				return False
			else:
				if i == 1:
					return False
				peak = A[i]
			prev = A[i]
		print(peak)
		return True if peak != -1 else False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		start = 0
		finish = len(A)
		print(len(A))
		for i in range(0, len(A) - 1):
			print(('i', i))
			if A[i] == A[i + 1]:
				return False
			elif A[i] > A[i + 1]:
				start = i
				print(('else1', start))
				break
		for j in range(0, len(A) - 1):
			print(('j', j))
			if A[len(A) - 1 - j] == A[len(A) - 2 - j]:
				return False
			elif A[len(A) - 1 - j] > A[len(A) - 2 - j]:
				print(('break2', len(A) - 1 - j, len(A) - 2 - j, A[len(A) - 1 - j], A[len(A) - 2 - j]))
				finish = len(A) - 1 - j
				break
		print(('s, f', start, finish))
		return start == finish and start > 0 and (finish < len(A))


class Solution:

	def __init__(self):
		self.f = True

	def impl(self, arr, i, incr):
		self.f = incr
		if i + 1 >= len(arr):
			return True
		if arr[i + 1] > arr[i] and (not incr):
			return False
		elif arr[i + 1] < arr[i] and incr:
			incr = False
		elif arr[i + 1] == arr[i]:
			return False
		return self.impl(arr, i + 1, incr)

	def validMountainArray(self, A) -> bool:
		if A == None or len(A) <= 2:
			return False
		if A[1] < A[0]:
			return False
		self.f = True
		result = self.impl(A, 0, True)
		if self.f:
			return False
		return result


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if not A or len(A) < 3:
			return False
		(l, r) = (0, len(A) - 1)
		while l < r:
			if A[l] < A[l + 1] and A[r - 1] > A[r]:
				l += 1
				r -= 1
			elif A[l] < A[l + 1]:
				l += 1
			elif A[r - 1] > A[r]:
				r -= 1
			else:
				return False
			print(l, r)
		if l == r and l != 0 and (r != len(A) - 1):
			return True
		else:
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		i = 1
		N = len(A)
		if N < 3:
			return False
		while i < N and A[i] > A[i - 1]:
			i += 1
		if i == 1 or i == N:
			return False
		while i < N and A[i] < A[i - 1]:
			i += 1
		return i == N


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) <= 2:
			return False
		else:
			t = 0
			(c1, c2) = (0, 0)
			for i in range(1, len(A) - 1):
				if A[i] == A[i + 1]:
					return False
					break
				elif A[i - 1] < A[i] < A[i + 1] or A[i - 1] > A[i] > A[i + 1] or A[i - 1] < A[i] > A[i + 1]:
					t += 1
					if A[i - 1] < A[i] < A[i + 1]:
						c1 += 1
					if A[i - 1] > A[i] > A[i + 1]:
						c2 += 1
			if t == len(A) - 2 and c1 < len(A) - 2 and (c2 < len(A) - 2):
				return True
			else:
				return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		nprev = A[0]
		for i in range(1, len(A)):
			if A[i] <= nprev:
				nprev = A[i - 1]
				start = i
				break
			nprev = A[i]
			if i == len(A) - 1:
				return False
		for i in range(start, len(A)):
			if A[i] >= nprev:
				return False
			nprev = A[i]
			if start == 1 and i == len(A) - 1:
				return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		maxIndex = A.index(max(A))
		if maxIndex == len(A) - 1 or maxIndex == 0:
			return False
		for i in range(maxIndex):
			if A[i] >= A[i + 1]:
				return False
		for i in range(maxIndex, len(A) - 1):
			if A[i] <= A[i + 1]:
				return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		increasing = True
		prev = -1
		if len(A) < 3:
			return False
		for (idx, i) in enumerate(A):
			print(prev, i, increasing)
			if i == prev:
				return False
			if increasing:
				if i < prev:
					increasing = False
					if idx == 1:
						return False
			elif i > prev:
				return False
			prev = i
		if increasing == True:
			return False
		return True


class Solution:

	def validMountainArray(self, arr: List[int]) -> bool:
		i = 0
		l = len(arr)
		while i + 1 < l and arr[i] < arr[i + 1]:
			i += 1
		if i == 0 or i == l - 1:
			return False
		while i + 1 < l and arr[i] > arr[i + 1]:
			i += 1
		return i == l - 1


class Solution(object):

	def validMountainArray(self, A):
		N = len(A)
		i = 0
		while i + 1 < N and A[i] < A[i + 1]:
			i += 1
		if i == 0 or i == N - 1:
			return False
		while i + 1 < N and A[i] > A[i + 1]:
			i += 1
		return i == N - 1


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) <= 2:
			return False
		i = 0
		N = len(A)
		while i < N and i + 1 < N and (A[i] < A[i + 1]):
			i += 1
		if i == 0 or i == N - 1:
			return False
		while i < N and i + 1 < N and (A[i] > A[i + 1]):
			i += 1
		if i == N - 1:
			return True
		return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		m = (0, 0)
		for i in range(0, len(A)):
			if A[i] > m[1]:
				m = (i, A[i])
		if m[0] == 0 or m[0] == len(A) - 1:
			return False
		for i in range(0, m[0] - 1):
			if A[i] >= A[i + 1]:
				return False
		for i in range(m[0], len(A) - 1):
			if A[i] <= A[i + 1]:
				return False
		return True


class Solution:

	def walkUp(self, A: List[int]) -> int:
		for (i, step) in enumerate(A[:-1]):
			if A[i] >= A[i + 1]:
				return i
		return len(A)

	def walkDown(self, A: List[int], top: int) -> bool:
		for (i, step) in enumerate(A[top:-1], start=top):
			if A[i] <= A[i + 1]:
				return False
		return True

	def validMountainArray(self, A: List[int]) -> bool:
		top = self.walkUp(A)
		if top == 0 or top == len(A):
			return False
		return self.walkDown(A, top)


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		switch = 0
		if A[0] > A[1]:
			return False
		for i in range(2, len(A)):
			if A[i] == A[i - 1]:
				return False
			if switch == 0 and A[i] < A[i - 1]:
				switch = 1
			elif switch == 1 and A[i] > A[i - 1]:
				return False
		if switch == 0:
			return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		N = len(A) - 1
		reached = False
		for i in range(N):
			if A[i] == A[i + 1]:
				return False
			if not reached:
				if A[i] > A[i + 1]:
					if i == 0:
						return False
					reached = True
			elif A[i] < A[i + 1]:
				return False
		return reached


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) >= 3:
			peak = max(A)
			if A.count(peak) == 1:
				peakInd = A.index(peak)
				incArr = A[:peakInd]
				decArr = A[peakInd + 1:]
				if len(incArr) > 0 and len(decArr) > 0:
					for i in range(1, len(incArr)):
						if incArr[i] <= incArr[i - 1]:
							return False
					for d in range(0, len(decArr) - 1):
						if decArr[d] <= decArr[d + 1]:
							return False
					return True
				else:
					return False
			else:
				return False
		else:
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		strict_inc = False
		strict_dec = False
		if len(A) > 2:
			for i in range(1, len(A)):
				if A[i] > A[i - 1]:
					if strict_dec:
						return False
					strict_inc = True
				elif A[i] < A[i - 1]:
					strict_dec = True
				else:
					return False
			if strict_inc and strict_dec:
				return True
			else:
				return False
		else:
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) in [0, 1, 2]:
			return False
		max_ele = max(A)
		if A.count(max_ele) > 1:
			return False
		index = A.index(max_ele)
		if index == len(A) - 1 or index == 0:
			return False
		for i in range(0, index):
			print(('values', A[i], A[i + 1]))
			print(('index', i, i + 1))
			if not A[i] < A[i + 1]:
				print('trig1')
				return False
		for i in range(len(A) - 1, index + 1, -1):
			print('hi')
			if not A[i] < A[i - 1]:
				print('trig2')
				return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		(i, j) = (0, len(A) - 1)
		while i < j:
			if A[i] < A[i + 1]:
				i += 1
			if A[j] < A[j - 1]:
				j -= 1
			elif i + 1 >= len(A) or A[i] >= A[i + 1]:
				break
		return i == j and 0 < i < len(A) - 1


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		diffs = [A[i + 1] - A[i] for i in range(len(A) - 1)]
		if 0 in diffs or diffs[0] < 0:
			return False
		peak = False
		for i in range(len(diffs) - 1):
			if diffs[i + 1] / abs(diffs[i + 1]) != diffs[i] / abs(diffs[i]):
				if peak == False:
					peak = True
				else:
					return False
		return peak


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		for i in range(len(A) - 1):
			if A[i] >= A[i + 1]:
				break
		for j in range(-1, -len(A), -1):
			if A[j] >= A[j - 1]:
				break
		return i == len(A) + j


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		n = len(A)
		if n < 3:
			return False
		changes = 0
		is_increasing = False
		is_decreasing = False
		for i in range(0, n - 1):
			if changes == 0:
				if A[i] > A[i + 1]:
					changes += 1
					is_decreasing = True
				elif A[i] == A[i + 1]:
					changes += 1
				else:
					is_increasing = True
			elif changes == 1:
				if A[i] <= A[i + 1]:
					changes += 1
				else:
					is_decreasing = True
			else:
				return False
		return changes < 2 and is_decreasing and is_increasing


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		arr = A
		i = 1
		while i < len(arr):
			if arr[i - 1] < arr[i]:
				i += 1
			else:
				break
		if i == 1 or i == len(arr):
			return False
		while i < len(arr):
			if arr[i - 1] > arr[i]:
				i += 1
			else:
				return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		up = True
		for i in range(1, len(A)):
			if A[i] == A[i - 1]:
				return False
			if up:
				if A[i] < A[i - 1]:
					if i == 1:
						return False
					up = False
			elif A[i] > A[i - 1]:
				return False
		return not up


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) < 3:
			return False
		if A[0] > A[1]:
			return False
		decreasing = False
		last = A.pop(0)
		while A:
			new = A.pop(0)
			print((new, last, decreasing))
			if new == last:
				return False
			if new > last and decreasing:
				print('early')
				return False
			if new < last and (not decreasing):
				decreasing = True
			last = new
		return decreasing


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		n = len(A)
		if n < 3:
			return False
		i = 0
		while i < n - 1 and A[i] < A[i + 1]:
			i += 1
		if i == 0 or i == n - 1:
			return False
		while i < n - 1 and A[i] > A[i + 1]:
			i += 1
		if i != n - 1:
			return False
		return True


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		passedPeak = False
		if len(A) <= 2 or A[0] > A[1]:
			return False
		for i in range(len(A) - 1):
			if A[i] == A[i + 1]:
				return False
			if passedPeak == True and A[i] < A[i + 1]:
				return False
			if passedPeak == False and A[i] > A[i + 1]:
				passedPeak = True
		if passedPeak:
			return True
		else:
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		inflection = None
		if len(A) > 3:
			for i in range(0, len(A) - 1):
				if inflection is not None:
					if A[i] < A[i + 1]:
						return False
				elif A[i] > A[i + 1]:
					inflection = i
			print(inflection, A[0:inflection], A[inflection:])
			if inflection is not None:
				if len(A[0:inflection]) and len(A[inflection:]):
					if len(set(A[0:inflection])) + len(set(A[inflection:])) == len(A):
						return True
					else:
						return False
				else:
					return False
					print(set(A[0:inflection]), len(A[0:inflection]), set(A[inflection:]), len(A[inflection:]))
					return False
			else:
				return False
		elif len(A) == 3:
			if A[0] < A[1] and A[1] > A[2]:
				return True
			else:
				return False
		else:
			return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		climb = True
		cs = 0
		fs = 0
		for i in range(1, len(A)):
			if climb == True:
				if A[i] > A[i - 1]:
					cs += 1
					continue
				elif A[i] == A[i - 1]:
					return False
				else:
					climb = False
			if climb == False:
				if A[i] < A[i - 1]:
					fs += 1
					continue
				else:
					return False
		if cs > 0 and fs > 0:
			return True
		return False


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if len(A) == 0 or len(A) == 1:
			return False
		idx = 0
		while idx < len(A) - 1 and A[idx] < A[idx + 1]:
			idx += 1
		if idx == 0 or idx == len(A) - 1:
			return False
		while idx < len(A) - 1 and A[idx] > A[idx + 1]:
			idx += 1
		print((idx, len(A)))
		return idx == len(A) - 1


class Solution:

	def validMountainArray(self, A: List[int]) -> bool:
		if not A or len(A) <= 2:
			return False
		increase = -1
		for i in range(1, len(A)):
			if A[i] > A[i - 1] and increase == -1:
				increase = 1
			if A[i] > A[i - 1] and increase == 1:
				continue
			elif A[i] < A[i - 1] and increase == 1:
				increase = 0
			elif A[i] < A[i - 1] and increase == 0:
				continue
			else:
				return False
		if increase != 0:
			return False
		return True