Problem:
 Score : 300 points    Problem Statement There are N people, conveniently numbered 1 through N .
They were standing in a row yesterday, but now they are unsure of the order in which they were standing.
However, each person remembered the following fact: the absolute difference of the number of the people who were standing to the left of that person, and the number of the people who were standing to the right of that person.
According to their reports, the difference above for person i is A_i .  Based on these reports, find the number of the possible orders in which they were standing.
Since it can be extremely large, print the answer modulo 10^9+7 .
Note that the reports may be incorrect and thus there may be no consistent order.
In such a case, print 0 .      Constraints  1≦N≦10^5  0≦A_i≦N-1         Input The input is given from Standard Input in the following format:  N  A_1  A_2  ...  A_N       Output Print the number of the possible orders in which they were standing, modulo 10^9+7 .        Sample Input 1 5
2 4 4 0 2      Sample Output 1 4  There are four possible orders, as follows:   2,1,4,5,3  2,5,4,1,3  3,1,4,5,2  3,5,4,1,2        Sample Input 2 7
6 4 0 2 4 0 2      Sample Output 2 0  Any order would be inconsistent with the reports, thus the answer is 0 .       Sample Input 3 8
7 5 1 1 7 3 5 3      Sample Output 3 16

Solution (Python):
from math import ceil

def solve(n, A):
    p = 10 ** 9 + 7
    nums = {n - 2 * i - 1: 0 for i in range(ceil(n / 2))}
    for a in A:
        if (a not in nums) or (a == 0 and nums[a] == 1) or (nums[a] == 2):
            return 0
        nums[a] += 1
    ret = 1
    for _ in range(n // 2):
        ret = (ret * 2) % p
    return ret

_n = int(input())
_A = map(int, input().split())
print(solve(_n, _A))

Solution (Python):
import collections

MOD = 10 ** 9 + 7
N = int(input())
A = list(map(int, input().split()))
ap = [0 for _ in range(N)]

for a in A:
	ap[a] += 1
	
flg = 1
if N % 2 == 0:
	for i in range(1, N, 2):
		if ap[i] != 2:
			flg = 0
			break
			
else:
	if ap[0] != 1:
		flg = 0
	else:
		for i in range(2, N, 2):
			if ap[i] != 2:
				flg = 0
				break
				

	
if not flg:
	print(0)
else:
	if N % 2 == 0:
		ans = pow(2, N // 2, MOD)
	else:
		ans = pow(2, (N - 1) // 2, MOD)
		
	print(ans)

Solution (Python):
from collections import Counter


def is_feasible(N, cntA):
    if N % 2 == 0:
        if len(cntA) != N // 2:
            return False

        for i in range(1, N, 2):
            if cntA[i] != 2:
                return False

        return True
    else:
        if len(cntA) != (N + 1) // 2:
            return False

        for i in range(0, (N + 1) // 2, 2):
            if i == 0:
                if cntA[i] != 1:
                    return False
            else:
                if cntA[i] != 2:
                    return False

        return True


MOD = 10 ** 9 + 7
N = int(input())
cntA = Counter(map(int, input().split()))

if is_feasible(N, cntA) is False:
    print(0)
else:
    if N % 2 == 0:
        ans = 1
        for i in range(N // 2):
            ans *= 2
            ans %= MOD
        print(ans % MOD)
    else:
        ans = 1
        for i in range(N // 2):
            ans *= 2
            ans %= MOD
        print(ans % MOD)

Solution (Python):
N = int(input())
A = [int(n) for n in input().split()]

def main():
    d = {}
    for a in A:
        if a not in d:
            d[a] = 0
        d[a] += 1
    ks =  all(map(lambda k: k % 2 == 0, d.keys())) or all(map(lambda k: k % 2 != 0, d.keys()))
    if 0 in d:
        d[0] += 1
    vs = all(map(lambda v: v == 2, d.values()))

    if ks and vs:
        n = N if N % 2 == 0 else N - 1
        n //= 2
        ans = 1
        for _ in range(n):
            ans *= 2
            ans %= 1000000007
    else:
        ans = 0
    print(ans)

if __name__ == '__main__':
    main()

Solution (Python):
N = int(input())
*a, = map(int, input().split())
a.sort()
ok = True
t = 1
if N % 2 == 1:
    if a.pop(0) != 0:
        ok = False
    t = 2

if ok:
    for i in range(0, len(a), 2):
        if t != a[i] or t != a[i+1]:
            ok = False
            break
        t += 2

if ok:
    print((2**((N-N % 2)//2)) % (10**9+7))
else:
    print(0)

Solution (Python):
import sys
n = int(input())
a = list(map(int, input().split()))


cnt = [0] * n
for x in a:
  cnt[x] += 1

ok = True
for i in range(0, n):
  if n % 2 == 1 and i % 2 == 0:
    if i == 0 and cnt[i] != 1 or i > 0 and cnt[i] != 2:
      ok = False
  elif n % 2 == 0 and i % 2 == 1:
    if cnt[i] != 2:
      ok = False

if not ok:
  print(0)
else:
  res = 1
  for i in range(0, n // 2):
    res *= 2
    res %= 1000000007
  print(res)

Solution (Python):
n = int(input())
a = list(map(int, input().split()))

import collections

c = collections.Counter(a)
f = 0
for i in c.items():
    if n % 2 != 0 and i[0] == 0 and i[1] == 1:
        pass
    elif i[1] == 2:
        pass
    else:
        f = 1
        break
if f == 1:
    print(0)
else:
    print((2 ** (n // 2)) % (10 ** 9 + 7))

Solution (Python):
N = int(input())
A = [int(a) for a in input().split()]

mod = 10**9+7
A.sort(reverse=True)
i = 0
ans = 1
while i < N-1:
    if A[i] == A[i+1] and A[i] == N-i-1:
        ans *= 2
        ans %= mod
        i += 2
    else:
        ans = 0
        break

if N%2 == 1 and A[-1] != 0:
    ans = 0

print(ans)

Solution (Python):
N = int(input())
A = sorted(list(map(int,input().split())))
amari = 10**9 + 7
ans = []
han = 0

if N % 2 == 0:
    han = 1
else:
    han = 0
    A.insert(0,0)


ans = list(int(i) for i in range(han,N,2))
ans += ans
ans.sort()

if ans == A:
    print(2**(N//2) % amari)
else:
    print("0")

Solution (Python):
base = 10**9 + 7
N = int(input())
A = list(map(int, input().split()))

counter = [0 for i in range(N)]

flag = True
for i in A:
  counter[i] += 1
  
for i in range(N):
  if counter[i] > 2:
    flag = False
if counter[0] > 1:
  flag = False
  
if flag:
  if N % 2 == 0:
    print(2**(N//2) % base)
  else:
    print(2**((N-1)//2) % base)
else:
  print(0)

Solution (Python):
n = int(input())
A = list(map(int, input().split()))
MOD = 10 ** 9 + 7
A.sort()
if n % 2 == 0:
  if A[::2] == A[1::2] == [i for i in range(1, n + 1, 2)]:
    ans = 2 ** (n // 2)
  else:
    ans = 0
else:
  if A == [0] or A[1::2] == A[2::2] == [i for i in range(2, n + 1, 2)]:
    ans = 2 ** (n // 2)
  else:
    ans = 0
print(ans % MOD)

Solution (Python):
import sys
import collections


input = sys.stdin.readline


def main():
    N = int(input())
    A = [int(x) for x in input().split()]
    c = collections.Counter(A)

    mod = 1
    if N & 1:
        mod = 0

    for k in c.keys():
        if mod == 0 and k == 0:
            continue

        if k % 2 != mod:
            print(0)
            break
        elif c[k] != 2:
            print(0)
            break
    else:
        print(pow(2, N // 2, 10 ** 9 + 7))



if __name__ == '__main__':
    main()

Solution (Python):

import sys
from collections import Counter
INF = float("inf")

MOD = 1000000007  


def solve(N: int, A: "List[int]"):
    c = Counter(A)
    flag = True
    if N % 2 == 0:
        for i in range(1, N, 2):
            if c[i] != 2:
                flag = False
        if flag == False:
            print(0)
            return
    else:
        for i in range(0, N, 2):
            if i == 0:
                if c[i] != 1:
                    flag = False
            elif c[i] != 2:
                flag = False
        if flag == False:
            print(0)
            return
    print(pow(2, N//2, MOD))
    return


def main():

    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    A = [int(next(tokens)) for _ in range(N)]  
    solve(N, A)


if __name__ == '__main__':
    main()

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
a_set = set(a)
if n%2==0:
  if n//2 != len(a_set) or 0 in a_set:
    print(0)
  else:
    print(2**len(a_set)%(10**9+7))
else:
  if n//2+1 != len(a_set) or a.count(0) != 1:
    print(0)
  else:
    print(2**(len(a_set)-1)%(10**9+7))

Solution (Python):
import sys
input = sys.stdin.buffer.readline
import collections

def main():
    N = int(input())
    A = list(map(int,input().split()))
    INF = 10**9+7
    
    c = collections.Counter(A)
    ans = True
    if N%2 == 0:
        for i in range(N//2):
            if c[2*i+1] != 2:
                ans = False
    else:
        for i in range(N//2):
            if c[2*i+2] != 2:
                ans = False
        if c[0] != 1:
            ans = False
            
    if ans:
        print(pow(2,(N//2),INF))
    else:
        print(0)
        

if __name__ == "__main__":
    main()

Solution (Python):
from collections import Counter

N = int(input())
A = list(map(int, input().split()))

numbers = Counter(list(range(not N % 2, N, 2)) * 2)
if N % 2:
    numbers[0] = 1
if Counter(A) == numbers:
    print(pow(2, (N // 2), int(10 ** 9 + 7)))
else:
    print(0)

Solution (Python):
n = int(input())
aList = sorted(list(map(int,input().split())))

if n == 1:
  if aList[0] != 0:
    print(0)
  else:
    print(1)
  exit(0)
if n % 2 != 0:
  if aList[0] != 0 and aList[1] == 0:
    print(0)
    exit(0)
  else:
    aList.pop(0)

for i in range(0,n-1,2):
  if i == 0:
    if aList[i] != aList[i+1]:
      print(0)
      exit(0)
  else:
    if aList[i] != aList[i+1] and aList[i] == aList[i-1]:
      print(0)
      exit(0)

result = 2
for i in range(1,n//2):
  result = (2*result)%  (10**9+7)

print(int(result))

Solution (Python):
N = int(input())
A = list(map(int, input().split()))

A_dict = dict()
if N % 2 == 0:
    for i in range(1, N, 2):
        A_dict[i] = 0
else:
    for i in range(0, N, 2):
        A_dict[i] = 0

for a in A:
    if a not in A_dict:
        print(0)
        exit()
    else:
        A_dict[a] += 1

for k, v in A_dict.items():
    if k == 0:
        if v != 1:
            print(0)
            exit()
    else:
        if v != 2:
            print(0)
            exit()
            
mod = 10**9+7
print(2 ** (N // 2) % mod)

Solution (Python):
import sys
input = sys.stdin.readline

N = int(input())
A = [int(x) for x in input().split()]
mod = 7 + 10 ** 9
from collections import Counter
c = Counter(A)
if N % 2 == 1:
    if c[0] != 1:
        print(0)
        sys.exit()
    for i in range(1, N):
        if i % 2 == 0 and c[i] != 2:
            print(0)
            sys.exit()
        elif i % 2 == 1 and c[i] != 0:
            print(0)
            sys.exit()
    print((2 ** (N // 2)) % mod)
else:
    for i in range(N):
        if i % 2 == 0 and c[i] != 0:
            print(0)
            sys.exit()
        elif i % 2 == 1 and c[i] != 2:
            print(0)
            sys.exit()
    print((2 ** (N // 2)) % mod)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
mod=10**9+7
if n%2==1:
    a.append(0)
a.sort()

odd=tuple(a[::2])
even=tuple(a[1::2])

if odd==even:
    ans=2**(n//2)
    ans%=mod
    print(ans)
else:
    print(0)

Solution (Python):
import math,string,itertools,fractions,heapq,collections,re,array,bisect,sys,random,time,copy,functools
from collections import deque

sys.setrecursionlimit(10**7)
inf = 10**20
mod = 10**9 + 7

DR = [1, -1, 0, 0]
DC = [0, 0, 1, -1]

def LI(): return [int(x) for x in sys.stdin.readline().split()]
def LI_(): return [int(x)-1 for x in sys.stdin.readline().split()]
def LF(): return [float(x) for x in sys.stdin.readline().split()]
def LS(): return sys.stdin.readline().split()
def I(): return int(sys.stdin.readline())
def F(): return float(sys.stdin.readline())
def S(): return input()
     
def main():
    N = I()
    A = LI()
    dic = collections.Counter()
    for a in A:
        dic[a] += 1
    even = False
    if N % 2 == 0:
        even = True
    cnt = 1
    n_element = 0
    if not even:
        for key, val in dic.items():
            if key == 0:
                continue
            if key % 2 > 0:
                cnt = 0
                break
            if val != 2:
                cnt = 0
                break
            n_element += 1

        for i in range(n_element):
            cnt = cnt * 2 % mod
        if dic[0] != 1:
            cnt = 0
    else:
        for key, val in dic.items():
            if key % 2 == 0:
                cnt = 0
                break
            if val != 2:
                cnt = 0
                break
            n_element += 1

        for i in range(n_element):
            cnt = cnt * 2 % mod
    print(cnt)

main()

Solution (Python):
MOD = 10**9 + 7
n = int(input())
a = sorted(list(map(int, input().split())))
if n % 2 == 1:
    b = [0]
    for i in range(1, n // 2 + 1):
        b.append(i * 2)
        b.append(i * 2)
else:
    b = []
    for i in range(n // 2):
        b.append(i * 2 + 1)
        b.append(i * 2 + 1)
if a != b:
    print(0)
else:
    print(pow(2, n//2, MOD))

Solution (Python):
def main():
    mod = 10 ** 9 + 7

    n = int(input())
    *a, = map(int, input().split())

    ctr = [0] * n
    for x in a:
        ctr[x] += 1

    if n % 2 == 1:
        if ctr[0] != 1:
            print(0)
            return
        for i in range(1, n):
            if (i % 2 == 0 and ctr[i] != 2) or (i % 2 == 1 and ctr[i] != 0):
                print(0)
                return

    else:
        for i in range(n):
            if (i % 2 == 0 and ctr[i] != 0) or (i % 2 == 1 and ctr[i] != 2):
                print(0)
                return

    print(pow(2, n // 2, mod))


if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter
n = int(input())
a = [int(i) for i in input().split()]
dct = Counter(a)
ans = 0
mod = 10**9+7

if n%2 == 0:
    r = range(1,n,2)
else:
    if dct[0] != 1:
        print(ans)
        exit()
    r = range(2,n,2)

for i in r:
    if dct[i] != 2:
        print(ans)
        exit()

ans = 2**(n//2)
print(ans%mod)

Solution (Python):
import sys
input = sys.stdin.readline
n=int(input())
a=list(map(int,input().split()))
from collections import Counter
c=Counter(a)
flg=True
if n%2==1:
    if c[0]!=1:
        print(0)
        exit()
for i in range(n//2):
    if c[i*2+n%2+1]!=2:
        flg=False
        break
ans=1
mod=10**9+7
if flg:
    for i in range(n//2):
        ans*=2
        ans%=mod
    print(ans)
else:
    print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))

from collections import Counter

ctr = Counter(A)

if N % 2 and ctr[0] != 1:
    print(0)
    exit()

if N % 2 == 0:
    for i in range(1, N ,2):
        if ctr[i] != 2:
            print(0)
            exit()
else:
    for i in range(2, N, 2):
        if ctr[i] != 2:
            print(0)
            exit()

MOD = 10 ** 9 + 7
ans = 2 ** (N//2) % MOD
print(ans)

Solution (Python):
m = 10**9+7
n = int(input())
a = list(map(int, input().split()))
check = True
if n%2 == 0:
    if 0 in a or len(set(a)) != n//2:
      check = False
else:
    if len([0 for i in a if i==0]) != 1 or len(set(a)) != n//2+1:
      check = False
      
if check:
  print(2**(n//2)%m)
else:
  print(0)

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
mod = 10**9+7
from collections import Counter
c = Counter(a)

for i in range(0+(n%2^1),n,2):
    if i == 0 and c.get(0,0) != 1:
        print(0)
        exit()
    elif i > 0 and c.get(i,0) != 2:
        print(0)
        exit()
print(2**(n//2) % mod)

Solution (Python):
import collections
mod = 10 ** 9 + 7
N = int(input())
A = list(map(int, input().split()))
a = collections.Counter(A)
a = a.most_common()[::-1]

if N % 2 == 0:
    for i in range(len(a)):
        if a[i][0] % 2 == 1 and a[i][1] == 2:
            pass
        else:
            print(0)
            exit()
    ans = (2 ** (N // 2)) % mod

else:
    for i in range(len(a)):
        if a[i][0] == 0:
            if a[i][1] == 1:
                pass
            else:
                print(0)
                exit()
        else:
            if a[i][0] % 2 == 0 and a[i][1] == 2:
                pass
            else:
                print(0)
                exit()
    ans = (2 ** (N // 2)) % mod 
print(ans)

Solution (Python):
mod = 10**9+7
N = int(input())
A = list(map(int,input().split()))
l = []
for i  in range(N):
    l.append(abs(N-2*i-1))
l.sort()
A.sort()
if l != A:
    ans = 0
else:
    ans = pow(2,N//2,mod)
print(ans)

Solution (Python):
from collections import Counter
N = int(input())
A = sorted(list(map(int,input().split())))
Ac = Counter(A)
if N%2 == 1:
    if A == [0]+sorted([2*i for i in range(1,N//2+1)]*2):
        flag = True
    else:
        flag = False
else:
    if A == sorted([1+2*i for i in range(N//2)]*2):
        flag = True
    else:
        flag = False
if flag:
    print((2**(N//2)%(10**9+7)))
else:
    print(0)

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
from collections import Counter
if N%2 == 0:
    for e in A:
        if e%2 == 0:
            print(0)
            exit()
else:
    for e in A:
        if e%2 == 1:
            print(0)
            exit()
L = Counter(A)
ans = 1
mod = 10**9+7
for key,value in L.items():
    if N%2 == 1 and key == 0 and value > 1:
        print(0)
        exit()
    if value > 2:
        print(0)
        exit()
    ans *= value%mod
print(ans%mod)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
mod = int(1e+9 + 7)
p = 0
D = {N-1-2*i: 0 for i in range((N+1)//2)}
for i in A:
  if i in D:
    D[i] += 1
s = 0
if sum(D[i] for i in D) == N and max(D[i] for i in D) == 2:
  if 0 in D:
    if D[0] == 1:
      s = 1
  else:
    s = 1
elif N == 1 and 0 in D:
  s = 1
if s == 1:
  p = 1
  for i in range(N//2):
    p *= 2
    p %= mod
print(p)

Solution (Python):
import collections
n = int(input())
*a, = map(int, input().split())

c = collections.Counter(a)
for k, v in c.items():
    if n%2 == 0:
        if v != 2:
            print(0)
            quit()
    else:
        if k != 0 and v != 2 or k == 0 and v != 1:
            print(0)
            quit()

print(2**(n//2)%(10**9+7))

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
A.sort()
inf = 10**9 + 7
if N%2 == 1:
    ans = 1
    for i in range((N-1)//2):
        ans = (ans*2)%inf
    for i in range(N):
        if A[i] != i+i%2:
            ans = 0
else:
    ans = 1
    for i in range(N//2):
        ans = (ans*2)%inf
    for i in range(N):
        if A[i] != i+1-i%2:
            ans = 0
print(ans)

Solution (Python):
import collections

MODBY = 7 + 10**9

N = int(input())
A_list = [int(e) for e in input().split()]

c = collections.Counter(A_list)

if N%2 == 0:
    for j in c.items():
        if j[1] != 2 or j[0]%2 != 1:
            print(0)
            break
    else:
        print(2**(N//2)%MODBY)
elif N%2 == 1:
    if c[0] != 1:
        print(0)
    else:
        for j in c.items():
            if (j[1] != 2 and j[0] != 0) or j[0]%2 != 0:
                print(0)
                break
        else:
            print(2**(N//2)%MODBY)

Solution (Python):


import sys
from collections import Counter

def input(): return sys.stdin.readline().strip()
def list2d(a, b, c): return [[c] * b for i in range(a)]
def list3d(a, b, c, d): return [[[d] * c for j in range(b)] for i in range(a)]
def list4d(a, b, c, d, e): return [[[[e] * d for j in range(c)] for j in range(b)] for i in range(a)]
def ceil(x, y=1): return int(-(-x // y))
def INT(): return int(input())
def MAP(): return map(int, input().split())
def LIST(N=None): return list(MAP()) if N is None else [INT() for i in range(N)]
def Yes(): print('Yes')
def No(): print('No')
def YES(): print('YES')
def NO(): print('NO')
sys.setrecursionlimit(10 ** 9)
INF = 10 ** 18
MOD = 10 ** 9 + 7

N = INT()
A = LIST()

C = Counter(A)
ans = 1
if N % 2 == 0:
    for i in range(1, N, 2):
        if C[i] != 2:
            print(0)
            exit()
        ans *= 2
        ans %= MOD
else:
    if C[0] != 1:
        print(0)
        exit()
    for i in range(2, N, 2):
        if C[i] != 2:
            print(0)
            exit()
        ans *= 2
        ans %= MOD
print(ans)

Solution (Python):
n=int(input())
a=list(map(int, input().split()))
k=(n+1)//2
b=[0]*(k)
for i in range(n):
  b[a[i]//2]+=1
out=1
if n%2==0:
  for i in range(k):
    if b[i]==2:
      out*=2
    else:
      out*=0
else:
  for i in range(1, k):
    if b[i]==2:
      out*=2
    else:
      out=0
  if b[0]!=1:
    out=0
print(out%(10**9+7))

Solution (Python):
N = int(input())
A = list(map(int, input().split()))

A.sort()
if N % 2 == 0:
    B = list(range(1, N, 2)) * 2
else:
    B = [0] + list(range(2, N, 2)) * 2
B.sort()

if A != B:
    print(0)
else:
    result = 1
    for i in range(N // 2):
        result *= 2
        result %= 1000000007
    print(result)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))


A_hash = {}

for i in A:
    if i in A_hash:
        A_hash[i] += 1
    else:
        A_hash[i] = 1

count = 0
for k, v in A_hash.items():
    if k == 0:
        continue
    if A_hash[k] != 2:
        print(0)
        exit()
    else:
        count += 1


ans = 1
for i in range(count):
    ans = ans * 2 % 1000000007
print(ans)

Solution (Python):
N = int(input())
A=[int(x) for x in input().split()]
H= True
A.sort()
if N%2==0:
  for i in range(N):
    if A[i] != 2*(i//2)+1:
      H=False
else:
  if A[0]!=0:
    H=False
  for i in range(1,N):
    if A[i]!=2*((i-1)//2)+2:
      H=False
print(2**(N//2)%(10**9+7) if H else '0')

Solution (Python):
import sys
input = sys.stdin.readline
N = int(input())
a = list(map(int, input().split()))
table = [0] * N
res = 1
mod = 10 ** 9 + 7
def no():
  print(0)
  exit(0)
for i in range(N):
  if a[i] >= N: no()
  table[a[i]] += 1
if table[0] != N % 2: no()
for i in range((N + 1) % 2, N, 2):
  if table[i] != 2:
    if i != 0: no()
  res *= table[i]
  res %= mod
print(res)

Solution (Python):
N=int(input())
A = list(map(int, input().split()))

A.sort(reverse=True)
ans = 2 ** (N//2)
for i in range(N-1):
    if (i%2 != 0):
        continue
    else:
        if(A[i] != N-(i+1) or A[i+1] != N-(i+1)):
            ans = 0

if (N%2 != 0 and A[-1] != 0):
    ans = 0

print(ans%(10**9+7))

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
MOD = 10**9+7

if N % 2 == 1: 
  A.append(0)

A.sort()
od = tuple(A[::2])
ev = tuple(A[1::2])

if od == ev:
  comb = (2**(N//2)) % MOD
  print(comb)
else:
  
  print(0)

Solution (Python):
n = int(input())
al = list(map(int,input().split()))

from collections import defaultdict
dic = defaultdict(int)
if n % 2 == 0:
   for a in al:
      dic[a] += 1
   for i in range(n//2):
      if dic[i*2+1] == 2:
         pass
      else:
         break
   else:
      print(2**(n//2)%(10**9+7))
      import sys
      sys.exit()
   print(0)
   import sys
   sys.exit()
else:
   for a in al:
      dic[a] += 1
   for i in range(n//2):
      if i == 0:
         if dic[i] == 1:
            pass
         else:
            break
      else:
         if dic[i*2] == 2:
            pass
         else:
            break
   else:
      print(2**(n//2)%(10**9+7))
      import sys
      sys.exit()
   print(0)
   import sys
   sys.exit()

Solution (Python):
def even_case(input_list) -> int:
    input_list.sort()

    if input_list[0] == 0: return 0


    for i in range(1, len(input_list), 2):
        if input_list[i] % 2 == 0 or input_list[i] != input_list[i-1]:
            return 0

    ans = 2 ** (n//2)

    return ans


def odd_case(input_list) -> int:
    input_list.sort()

    if input_list[0] != 0: return 0

    if len(input_list) == 1: return 1

    if input_list[1] == 0: return 0

    for i in range(2, len(input_list), 2):
        if input_list[i] % 2 == 1 or input_list[i] != input_list[i-1]:
            return 0

    ans = 2 ** ((n-1) // 2)

    return ans

n = int(input())
input_list = list(map(int, input().split()))
math = 10 ** 9 + 7

if n % 2 == 0:
    result = even_case(input_list)
else:
    result = odd_case(input_list)

print(result % math)

Solution (Python):
n=int(input())
numbb=input().split(' ')
numb=[]
for i in numbb:
    numb.append(int(i))
numb=sorted(numb)

if(n==len(numb)):
    if(n%2!=0):
        temp=[]
        temp.append(0)
        strt=2
        for i in range(0,int(n/2)):
            temp.append(strt)
            temp.append(strt)
            strt+=2
        if(temp==numb):
            
            print(pow(2,len(set(numb))-1)%(1000000007))
        else:
            print(0)
    if(n%2==0):
        temp=[]
        strt=1
        for i in range(0,int(n/2)):
            temp.append(strt)
            temp.append(strt)
            strt+=2
        if(temp==numb):
            
            
            print((pow(2,len(set(numb)))%(1000000007)))
        else:
            print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
A.sort()
isOK = True
BIG_PRIME = 1000000007

if N % 2: 
    for i in range(0, N - 2, 2):
        if A[i] != i:
            isOK = False
            break
        if A[i + 1] != i + 2:
            isOK = False
            break
    if A[N - 1] != N - 1:
        isOK = False
    num = (N - 1) // 2
else: 
    for i in range(0, N, 2):
        if A[i] != i + 1:
            isOK = False
            break
        if A[i + 1] != i + 1:
            isOK = False
            break
    num = N // 2

if isOK:
    ans = 1
    for _ in range(num):
        ans *= 2
        ans %= BIG_PRIME
    print(str(ans))
else:
    print("0")

Solution (Python):
import sys
input = sys.stdin.readline

N = int(input())
A = [int(i) for i in input().split()]

from collections import Counter

for key,count in sorted(Counter(A).items(), key=lambda x:x[0]):
    if key == 0 and N % 2 == 1:
        continue
    if count == 2 and key % 2 != N % 2:
        continue
    print(0)
    exit()

if N % 2 == 1:
    N -= 1

print(2 ** (N//2) % (10**9 + 7))

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
A.sort()
if N%2 == 0:
  check=[2*i+1 for i in range((N-1)//2+1)]*2
  check.sort()
else:
  check=[2*(i+1) for i in range(N//2)]*2
  check.append(0)
  check.sort()
if check == A:
  print((2**(N//2))%(10**9+7))
else:
  print(0)

Solution (Python):
n = int(input())
L = list(map(int,input().split()))
L.sort()
mod = 10**9+7
if len(L)%2 == 0 and len(set(L))*2 == len(L):
    print(2**len(set(L))%mod)
elif len(L)%2 == 0 and len(set(L))*2 != len(L):
    print(0)
elif len(L)%2 == 1: 
    if L.count(0) == 1:
        L.pop(0)
        if len(set(L))*2 == len(L):
            print(2**(len(set(L)))%mod)
    else:
        print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
mod = 10 ** 9 + 7

A.sort()
if N % 2 == 0:
    
    
    if A[0:N:2] != A[1:N+1:2]:
        print(0)
        exit(0)
else:
    if A[0] != 0:
        print(0)
        exit()
    if A[1:N-1:2] != A[2:N:2]:
        print(0)
        exit()

print(2 ** (N // 2) % mod)

Solution (Python):

import sys, math, itertools, collections, bisect
input = lambda: sys.stdin.buffer.readline().rstrip().decode('utf-8')
inf = float('inf')
ans = 0 ;count = 0 ;pro = 1
mod=10**9+7
n=int(input())
A=list(map(int,input().split()))
C=collections.Counter(A)
if n%2==1:
    if C[0]!=1:
        print(0)
        exit()
    else:
        a=2
else:
    if C[1]!=2:
        print(0)
        exit()
    else:
        a=3
for i in range(a,n,2):
    if C[i]!=2:
        print(0)
        exit()
print(pow(2,n//2,mod))

Solution (Python):
import collections

N = int(input())

A = list(map(int, input().split()))

mod = 10**9+7


c = collections.Counter(A)





if len(A) ==1 and A[0]==0:
    print(1)

elif len(A)%2==0:
    if list(c.values()).count(2) == (len(A) // 2 ):
        print(2**(len(c.values()))%mod)
    else:
        print(0)
else:
    if list(c.values()).count(2) == (len(A) // 2 ) and c[0] == 1:
        print((2**(len(c.values())-1))%mod)
    else:
        print(0)

Solution (Python):
n=int(input())
L=list(map(int,input().split()))
mod=10**9+7
if n==1:
    if L==[0]:
        print(1)
    else:
        print(0)
elif n%2==0:
    M=[2*i+1 for i in range(n//2)]
    M=M+M
    M.sort()
    L.sort()
    print((2**(n//2))%mod if L==M else 0)
else:
    M=[2*i for i in range(n//2 +1)]
    M=M+M[1:]
    M.sort()
    L.sort()
    print((2**(n//2))%mod if L==M else 0)

Solution (Python):
import sys
from collections import Counter

MOD = 10 ** 9 + 7

n, *a = map(int, sys.stdin.read().split())

def main():
    c = Counter(a)
    if n & 1:
        if c.get(0, 0) != 1:
            return 0
    for i in range(1 + (n & 1), n, 2):
        if c.get(i, 0) != 2:
            return 0

    return pow(2, n // 2, MOD)
    
if __name__ == '__main__':
    ans = main()
    print(ans)

Solution (Python):
import sys
from collections import Counter

MOD = 10 ** 9 + 7

n, *a = map(int, sys.stdin.read().split())

def main():
    c = Counter(a)
    if n & 1:
        if c.get(0, 0) != 1:
            return 0
        for i in range(2, n, 2):
            if c.get(i, 0) != 2:
                return 0
    else:
        for i in range(1, n, 2):
            if c.get(i, 0) != 2:
                return 0

    return pow(2, n // 2, MOD)
    
if __name__ == '__main__':
    ans = main()
    print(ans)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
b=sorted(a)
for i in range(n):
  if n%2==0:
    if i//2*2+1!=b[i]:
      print(0)
      exit()
  if n%2==1:
    if (i+1)//2*2!=b[i]:
      print(0)
      exit()
print(2**(n//2)%(10**9+7))

Solution (Python):
n = int(input())
l = list(map(int, input().split()))

if n%2 == 0:
  l_ = [0]*(n//2)
  for i in range(n):
    l_[(n-(l[i])-1)//2] += 1
  for j in range(len(l_)):
    if l_[j] != 2:
      print(0)
      exit()
  else:
    print((2**(n//2))%(10**9+7))

else:
  l_ = [0]*(n//2+1)
  for i in range(n):
    l_[(n-(l[i])-1)//2] += 1
  for j in range(len(l_)):
    if j != len(l_)-1: 
      if l_[j] != 2:
        print(0)
        exit()
    else:
      if l_[j] != 1:
        print(0)
        exit()
  else:
    print((2**(n//2))%(10**9+7))

Solution (Python):
n = int(input())
l = list(map(int, input().split()))

if n%2 == 0:
  l_ = [0]*(n//2)
  for i in range(n):
    l_[(n-(l[i])-1)//2] += 1
  for j in range(len(l_)):
    if l_[j] != 2:
      print(0)
      exit()
  else:
    print((2**(n//2))%(10**9+7))

else:
  l_ = [0]*(n//2+1)
  for i in range(n):
    l_[(n-(l[i])-1)//2] += 1
  for j in range(len(l_)):
    if j != len(l_)-1: 
      if l_[j] != 2:
        print(0)
        exit()
    else:
      if l_[j] != 1:
        print(0)
        exit()
  else:
    print((2**(n//2))%(10**9+7))

Solution (Python):
n = int(input())
a = list(map(int, input().split()))

from collections import Counter
c = Counter(a)
if n % 2 == 1:
    ans = 1
    for i in range(n // 2 + 1):
        ii = 2 * i
        if i == 0 and c[ii] == 1:
            ans *= 1
        elif i != 0 and c[ii] == 2:
            ans *= 2
        else:
            ans *= 0
        ans %= (10 ** 9 + 7)
else:
    ans = 1
    for i in range(n // 2):
        ii = 2 * i + 1
        if c[ii] == 2:
            ans *= 2
        else:
            ans *= 0
        ans %= (10 ** 9 + 7)
print(ans)

Solution (Python):
import sys
import math

if sys.platform =='ios':
	sys.stdin=open('Untitled.txt')
input = sys.stdin.readline
def INT(): return int(input())
def MAP(): return [int(s) for s in input().split()]
MOD = 10**9+7

N = INT()
A = MAP()

A.sort()


s = 0 if N%2 else 1
e = N if N%2 else N+1

for i in range(s, e):
	t = math.ceil(i/2)*2
	if not N%2: t -= 1
	if t != A[i-s]:
		print(0)
		break
else:
	print(2**(N//2)%MOD)