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):
n=int(input())
a=list(map(int,input().split()))
import collections
d=collections.defaultdict(int)
for i in a:
    d[i]+=1
mod=(10**9)+7

if n%2==0:
    x=[i for i in d.keys()]
    x=sorted(x)
    for i in range(len(x)):
        if i==0 and (x[i]!=1 or d[x[i]]!=2):
            print(0)
            exit()
        elif i>=1:
            if x[i]-x[i-1]!=2 or d[x[i]]!=2:
                print(0)
                exit()
    print((2**len(x))%mod)
else:
    x=[i for i in d.keys()]
    x=sorted(x)
    if x[0]!=0 or d[x[0]]!=1:
        print(0)
        exit()
    x=x[1:]
    for i in range(len(x)):
        if i==0 and (x[i]!=2 or d[x[i]]!=2):
            print(0)
            exit()
        elif i>=1:
            if x[i]-x[i-1]!=2 or d[x[i]]!=2:
                print(0)
                exit()
    print((2**len(x))%mod)

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

x = N // 2
ans = pow(2, x, mod)

c = Counter(A)
if N & 1:
    for i in range(0, N, 2):
        if i == 0 and c[i] == 1:
            continue
        if c[i] == 2:
            continue
        ans = 0
else:
    for i in range(1, N, 2):
        if c[i] == 2:
            continue
        ans = 0

print(ans)

Solution (Python):
def main():
    N = int(input())
    A = [int(i) for i in input().split()]
    MOD = 10**9 + 7
    from collections import Counter
    c = Counter(A)
    
    for k, v in c.items():
        if k != 0 and v != 2:
            return print(0)
    if N & 1 and c[0] != 1:
        return print(0)

    if N & 1:
        ma = max(A)//2
    else:
        ma = (max(A) + 1)//2
    print(pow(2, ma, MOD))


if __name__ == '__main__':
    main()

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

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

Solution (Python):
import sys
sys.setrecursionlimit(10**6)
from math import floor,ceil,sqrt,factorial,log
from heapq import heappop, heappush, heappushpop
from collections import Counter,defaultdict,deque
from itertools import accumulate,permutations,combinations,product,combinations_with_replacement
from bisect import bisect_left,bisect_right
from copy import deepcopy
from operator import itemgetter
from fractions import gcd
mod = 10 ** 9 + 7
inf = float('inf')
ninf = -float('inf')
 

def ii(): return int(sys.stdin.readline().rstrip()) 
def mii(): return map(int,sys.stdin.readline().rstrip().split())
def limii(): return list(mii()) 
def lin(n:int): return [ii() for _ in range(n)]
def llint(n: int): return [limii() for _ in range(n)]

def ss(): return sys.stdin.readline().rstrip() 
def mss(): return sys.stdin.readline().rstrip().split()
def limss(): return list(mss()) 
def lst(n:int): return [ss() for _ in range(n)]
def llstr(n: int): return [limss() for _ in range(n)]





n=ii()
arr0=limii()

arr=Counter(arr0)

ai=list(arr.items())
ai.sort()
if n%2==0:
    cnt=0
    for p,i in enumerate(range(1,n,2)):

        if ai[p][0]==i and ai[p][1]==2:
            cnt+=1
    if cnt==n//2:
        print((2**(n//2))%mod)
    else:
        print(0)
else:
    cnt=0
    for p,i in enumerate(range(0,n,2)):
        if p==0:
            if ai[p][0]==i and ai[p][1]==1:
                cnt+=1
        else:        
            if ai[p][0]==i and ai[p][1]==2:
                cnt+=1
    if (n+1)//2==cnt:
        print((2**(cnt-1))%mod)
    else:
        print(0)

Solution (Python):

from math import ceil
N = int(input())
mod = 10**9 + 7
A = list(map(int, input().split()))
A.sort()
flag = True
if len(set(A)) != ceil(N / 2):
    flag = False
if N % 2 == 1:
    if A[0] != 0:
        flag = False
    else:
        for i in range(1, N, 2):
            if A[i] != A[i+1] or A[i] % 2 == 1:
                flag = False
else:
    for i in range(N, 2):
        if A[i] != A[i+1] or A[i] % 2 == 0:
            flag = False
ans = 1
if flag:
    for i in range(N//2):
        ans *= 2
        ans %= mod
else:
    ans = 0
print(ans)

Solution (Python):
N = int(input())
A = [int(a) for a in input().split()]
A.sort()
mod = 7 + 10 ** 9
count = 1
if N % 2 == 0:
    for i, a in enumerate(A):
        if a != 2 * (i // 2) + 1: 
            count = 0
            break
        if i % 2 == 1:
            count *= 2
            count %= mod
else:
    for i, a in enumerate(A):
        if a != 2 * ((i + 1) // 2):
            count = 0
            break
        if i % 2 == 1:
            count *= 2
            count %= mod
print(count)

Solution (Python):
N = int(input())

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

data = [0] * N
possible = True
MOD = 10**9+7

for a in A:
	data[a] += 1

if N % 2 == 0:
	for i in range(1,N,2):
		if data[i] != 2:
			possible = False
			break
else:
	if data[0] == 1:
		for i in range(2,N,2):
			if data[i] != 2:
				possible = False
				break
	else:
		possible = False

if possible:
	if N % 2 == 0:
		num = N // 2
	else:
		num = (N-1)//2
	ans = 1
	for i in range(num):
		ans = ans * 2 % MOD
		ans %= MOD

	print(ans)
else:
	print(0)

Solution (Python):
import collections


def calc_ans(n):
    ans = 1
    for i in range(n//2):
        ans = ans*2 % (10**9+7)
    print(ans)


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

c = collections.Counter(A)

if n % 2 == 0:
    for i in range(1, n, 2):
        if c[i] != 2:
            print(0)
            break
    else:
        calc_ans(n)
else:
    for i in range(0, n, 2):
        if (i == 0 and c[i] != 1) or (i != 0 and c[i] != 2):
            print(0)
            break
    else:
        calc_ans(n)

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

if n%2==1:
    sentou = a.pop(0)
    if sentou!=0:
        print("0")
        exit()
    nxt=2
else:
    nxt=1

ans=1
i=0
while i < len(a):
    if a[i] == nxt and a[i+1] == nxt:
        ans*=2
        ans%=10**9+7
        nxt+=2
        i+=2
    else:
        print("0")
        exit()
print(ans)

Solution (Python):
import sys
from numpy import *
n, *a = map(int, sys.stdin.read().split())
a = int_(bincount(a, [1] * n, n))
print(pow(2, n // 2, 10 ** 9 + 7) if not a[0] > (n & 1) and all([x == 2 or x == 0 for x in a[1:]]) else 0)

Solution (Python):
import sys

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

mod = 10 ** 9 + 7

count = [0] * N
for i in a:
    count[i] += 1
count[0] += 1
for i in count[1-N%2::2]:
    if i != 2:
        print(0)
        sys.exit()
s = N // 2
print(pow(2, s, mod))

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

exist = True
if N%2 == 0:
    for i in range(N):
        if A[i] != (i // 2)*2 + 1:
            exist = False
            break
    
    if exist == True:
        ans = 1
        for i in range(N//2):
            ans *= 2
            ans %= 10**9 + 7
        print(ans)
    else:
        print(0)
else:
    for i in range(N):
        if A[i] != ((i + 1) // 2)*2:
            exist = False
            break
    if exist == True:
        ans = 1
        for i in range((N-1)//2):
            ans *= 2
            ans %= 10**9 + 7
        print(ans)
    else:
        print(0)

Solution (Python):
import sys


N, *A = map(int, open(0).read().split())
MOD = 10 ** 9 + 7

A.sort()

ret = 1
if N % 2 == 0:
  for i, (a1, a2) in enumerate(zip(*[iter(A)]*2)):
    i = 2*i + 1
    if i == a1 and i == a2:
      ret *= 2
      ret %= MOD
    else:
      print(0)
      sys.exit()
else:
  if A[0] != 0:
    print(0)
    sys.exit()
  else:
      for i, (a1, a2) in enumerate(zip(*[iter(A[1:])]*2), 1):
        i *= 2
        if i == a1 and i == a2:
          ret *= 2
          ret %= MOD
        else:
          print(0)
          sys.exit()
          
print(ret)

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

ans = 1
A.sort()
if N % 2 == 1 and not A.count(0) == 1:
    ans = 0

s = -1
if N % 2 == 1:
    A.remove(0)
    s = 2
else:
    s = 1

for i in range(0, len(A), 2):
    if A[i] == A[i + 1] == s:
        ans *= 2
    else:
        ans = 0
    s += 2
    
print(ans % 1000000007)

Solution (Python):
n = int(input())

lst1 = list(map(int,input().split()))

dic1 = dict()
oe = 1
if n%2 == 1:
    oe = 0
for i in range(oe,n,2):
    dic1[i] = 0

for i in lst1:
    if i in dic1:
        dic1[i] += 1
    else:
        print(0)
        exit()

if oe == 0:
    if dic1[0] != 1:
        print(0)
        exit()

ans = 1
for i in dic1.values():
    if i == 2:
        ans*=2
    elif i == 0 or i > 2:
        ans = 0
        break
print(ans%(10**9+7))

Solution (Python):

import sys
import math
import os
import itertools
import _collections
import string
from functools import lru_cache
import heapq

class cin():
    def int():
        return int(sys.stdin.readline().rstrip())
    def string():
        return sys.stdin.readline().rstrip()
    def mapInt():
        return [int(x) for x in cin.string().split()]
    def stringList(n):
        return [input() for i in range(n)]
    def intListList(n):
        return [cin.mapInt() for i in range(n)]
    def intColsList(n):
        return [int(input()) for i in range(n)]
        
class Math():
    def gcd(a,b):
        if b == 0:
            return a
        return Math.gcd(b,a % b)
    def lcm(a,b):
        return (a * b) // Math.gcd(a,b)
    def roundUp(a,b):
        return -(-a // b)
    def toUpperMultiple(a,x):
        return Math.roundUp(a,x) * x
    def toLowerMultiple(a,x):
        return (a // x) * x
    def nearPow2(n):
        if n <= 0:
            return 0
        if n & (n - 1) == 0:
            return n
        ret = 1
        while(n > 0):
            ret <<= 1
            n >>= 1
        return ret
    def isPrime(n):
        if n < 2:
            return False
        if n == 2:
            return True
        if n % 2 == 0:
            return False
        d = int(n ** 0.5) + 1
        for i in range(3,d + 1,2):
            if n % i == 0:
                return False
        return True


MOD = int(1e09) + 7

def main():
    N = cin.int()
    A = cin.mapInt()
    A.sort()
    ans = 1
    for i in range(N % 2,N,2):
        if A[i] == A[i + 1] and A[i] == i + 1:
            ans *= 2
            ans %= MOD
        else:
            ans = 0
    print(ans)
    return

if __name__ == "__main__":
    main()

Solution (Python):

import sys
import math
import os
import itertools
import _collections
import string
from functools import lru_cache
import heapq

class cin():
    def int():
        return int(sys.stdin.readline().rstrip())
    def string():
        return sys.stdin.readline().rstrip()
    def mapInt():
        return [int(x) for x in cin.string().split()]
    def stringList(n):
        return [input() for i in range(n)]
    def intListList(n):
        return [cin.mapInt() for i in range(n)]
    def intColsList(n):
        return [int(input()) for i in range(n)]
        
class Math():
    def gcd(a,b):
        if b == 0:
            return a
        return Math.gcd(b,a % b)
    def lcm(a,b):
        return (a * b) // Math.gcd(a,b)
    def roundUp(a,b):
        return -(-a // b)
    def toUpperMultiple(a,x):
        return Math.roundUp(a,x) * x
    def toLowerMultiple(a,x):
        return (a // x) * x
    def nearPow2(n):
        if n <= 0:
            return 0
        if n & (n - 1) == 0:
            return n
        ret = 1
        while(n > 0):
            ret <<= 1
            n >>= 1
        return ret
    def isPrime(n):
        if n < 2:
            return False
        if n == 2:
            return True
        if n % 2 == 0:
            return False
        d = int(n ** 0.5) + 1
        for i in range(3,d + 1,2):
            if n % i == 0:
                return False
        return True


MOD = int(1e09) + 7

def main():
    N = cin.int()
    A = cin.mapInt()
    A.sort()
    ans = 1
    if N % 2 == 0:
        for i in range(0,N,2):
            if A[i] == A[i + 1] and A[i] == i + 1:
                ans *= 2
                ans %= MOD
            else:
                ans = 0
    else:
        if A[0] != 0:
            ans = 0
        for i in range(1,N,2):
            if A[i] == A[i + 1] and A[i] == i + 1:
                ans *= 2
                ans %=MOD
            else:
                ans = 0
    print(ans)
    return

if __name__ == "__main__":
    main()

Solution (Python):
import math

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

if N % 2 == 1:
  B = [0] * N
  for i in range(1,N):
    b = math.ceil(i / 2) * 2
    B[i] = b
else:
  B = [0] * N
  for i in range(N):
    b = math.floor(i / 2) * 2 + 1
    B[i] = b

if A == B:
  if N % 2 == 1:
    n = (N - 1) // 2
  else:
    n = N // 2
  print(2 ** n % (10 ** 9 + 7))
else:
  print(0)

Solution (Python):
import collections
N=int(input())
A=list(map(int,input().split()))
A=collections.Counter(A)
mod = 10**9 + 7
for i in range(1,N,2) if N%2==0 else range(2,N,2):
    if A[i]!=2:
        print(0)
        exit()
if N%2==1:
    if not 0 in A or A[0]!=1:
        print(0)
        exit()
print((2**((N-N%2)//2)) % mod)

Solution (Python):
from collections import Counter
import sys

n = int(input())
C = Counter(list(map(int, input().split())))

if n % 2 == 0:
    for key in C.keys():
        if C[key] != 2:
            print(0)
            sys.exit()
    print(pow(2,n//2,10**9+7))
else:
    for key in C.keys():
        if key == 0:
            if C[key] != 1:
                print(0)
                sys.exit()
        else:
            if C[key] != 2:
                print(0)
                sys.exit()
    print(pow(2,n//2,10**9+7))

Solution (Python):
from collections import Counter
N=int(input())
A=[int(a) for a in input().split()]
MOD=10**9+7

C=Counter(A)
i=1+(N&1)
while i<=N-1:
    if C[i]!=2:
        print(0)
        exit()
    i+=2

print(pow(2,N//2,MOD))

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

if N % 2 == 0:
    A_list = []
    for i in range(1, N, 2):
        A_list.extend([i, i])
else:
    A_list = [0]
    for i in range(2, N, 2):
        A_list.extend([i, i])
if A != A_list:
    print(0)
else:
    print(2**(N//2) % (10**9+7))

Solution (Python):
N, *A = map(int, open(0).read().split())
A = sorted(A)
MOD = 1000000007
if N & 1 != 0:
  K = 2
  F = True
  for i in range(1, N, 2):
    if A[i] != A[i+1] or A[i] != K:
      F = False
      break
    K += 2
  if A[0] != 0:
    F = False
  print(2 ** (N // 2) % MOD if F else 0)
else:
  K = 1
  F = True
  for i in range(0, N, 2):
    if A[i] != A[i+1] or A[i] != K:
      F = False
      break
    K += 2
  print(2 ** (N // 2) % MOD if F else 0)

Solution (Python):
import sys


def solve():
    readline = sys.stdin.buffer.readline
    mod = 10 ** 9 + 7
    n = int(readline())
    a = list(map(int, readline().split()))
    a.sort()
    t = 0
    if n % 2 == 0:
        t = 1
    for i in range(n):
        if i % 2 == n % 2 and i != 0:
            t += 2
        if a[i] != t:
            print(0)
            exit()
    print((2 ** (n // 2)) % mod)


if __name__ == '__main__':
    solve()

Solution (Python):
from collections import Counter
MOD = 10**9+7
N = int(input())
A = [int(i) for i in input().split()]
f0 = False
b = N & 1 ^ 1
c = Counter(A)
ans = 1
for n in range(N-1, 0, -2):
    if c[n] != 2:
        break
    ans *= 2
    ans %= MOD
else:
    if c[0] == N & 1:
        print(ans)
        exit()
print(0)

Solution (Python):
import collections
n = int(input())
a = list(map(int, input().split()))
dd = collections.defaultdict(int)
correct = []
if n % 2 == 1:
    correct.append(0)
    for i in range((n - 1) // 2):
        correct.append(2 * i + 2)
        correct.append(2 * i + 2)
else:
    correct.append(1)
    correct.append(1)
    for i in range(n // 2):
        correct.append(2 * i + 3)
        correct.append(2 * i + 3)
a.sort()
correct.sort()
for i in range(n):
    if a[i] != correct[i]:
        print(0)
        exit()
for i in range(n):
    dd[str(a[i])] += 1
ans = 1
for k in dd.keys():
    if dd[k] >= 2:
        ans *= 2
        ans %= 10 ** 9 + 7
print(ans)

Solution (Python):
def solve():
    N = int(input())
    cnt = [0] * N
    for A in map(int, input().split()):
        if A < N and (N + A) % 2 == 1 and (A > 0 and cnt[A] < 2 or A == 0 and cnt[A] < 1):
            cnt[A] += 1
        else:
            return 0
    return pow(2, N // 2, 10**9 + 7)
print(solve())

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

if c.most_common()[0][1] > 2:
    print(0)
elif c.most_common()[-1][1] == 1 and c[0] != 1:
    print(0)
elif n % 2 == 1 and c[0] != 1:
    print(0)
else:
    print(2 ** (len(c)-1) % mod if n % 2 == 1 else 2 ** len(c) % mod)

Solution (Python):
n = int(input())
l = [0] * n
for i in map(int,input().split()):
  l[i] += 1
if n % 2 == 0:
  al = [0] * n
  for i in range(1,n+1,2):
    al[i] = 2
  if l == al:
    print(pow(2,n//2,10**9+7))
  else:
    print(0)
else:
  al = [0] * n
  al[0] = 1
  for i in range(2,n+1,2):
    al[i] = 2
  if l == al:
    print(pow(2,n//2,10**9+7))
  else:
    print(0)

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

Solution (Python):
from collections import Counter
mod=10**9+7
n=int(input())
A=list(map(int,input().split()))
Count=sorted(Counter(A).items())
cnt=0
if n%2==1:
    if Count.pop(0)[1]==1:
        point=2
        for v,m in Count:
            if v==point and m==2:
                cnt +=1
                point +=2
        print((2**cnt)%mod)
    else:print(0);exit()
else:
    point=1
    for v,m in Count:
        if v==point and m==2:
            cnt +=1
            point +=2
        else:print(0);exit()
    print((2**cnt)%mod)

Solution (Python):
from collections import Counter
mod=10**9+7
n=int(input())
A=list(map(int,input().split()))
Count=sorted(Counter(A).items())
cnt=0
if n%2==1:
    if Count.pop(0)[1]==1 and len(Count)==n//2:
        point=2
        for v,m in Count:
            if v==point and m==2:
                cnt +=1
                point +=2
        print((2**cnt)%mod)
    else:print(0);exit()
else:
    point=1
    for v,m in Count:
        if v==point and m==2:
            cnt +=1
            point +=2
        else:print(0);exit()
    print((2**cnt)%mod)

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

mod=10**9+7

A.sort()
f=True
if N%2==1:
    if A[0]!=0:
        f=False
    else:
        for i in range(1,N,2):
            if not (A[i]==2*(i+1)//2 and A[i+1]==2*(i+1)//2):
                f=False
                break
elif N%2==0:
    for i in range(0,N,2):
        if not (A[i]==2*(i//2)+1 and  A[i+1]==2*(i//2)+1):
            f=False
            break

if f:
    print(2**(N//2)%mod)
else:
    print(0)

Solution (Python):
from collections import Counter

mod = int(1e9 + 7)
n = int(input())
A = list(map(int, input().split()))
c = Counter(A)

if n % 2 == 1:
    
    if 0 not in c or c[0] != 1:
        print(0)
        exit()



for i in range(n // 2):
    x = i * 2 + (1 if n % 2 == 0 else 2)
    if x not in c or c[x] != 2:
        print(0)
        exit()


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

Solution (Python):
from collections import Counter
lim=10**9+7
N=int(input())
A=[int(i) for i in input().split()]
if N % 2 == 0:
    if Counter(A) == {2*i+1:2 for i in range(N//2)}:
        print(pow(2,(N//2),lim))
    else:
        print(0)
else:
    if Counter(A) == {2*i if i>0 else 0:2 if i>0 else 1 for i in range((N+1)//2)}:
        print(pow(2,(N-1)//2,lim))
    else:
        print(0)

Solution (Python):
from collections import Counter
lim=10**9+7
N=int(input())
A=[int(i) for i in input().split()]
if N % 2 == 0:
    if Counter(A) == {2*i+1:2 for i in range(N//2)}:
        print(2**(N//2)%lim)
    else:
        print(0)
else:
    if Counter(A) == {2*i if i>0 else 0:2 if i>0 else 1 for i in range((N+1)//2)}:
        print(2**((N-1)//2)%lim)
    else:
        print(0)

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

a.sort()

if n%2==0:
    a.sort()
    for i in range(n//2):
        if a[i*2]!=a[i*2+1] or a[i*2]!=2*i+1 or a[i*2+1]!=2*i+1:
            print(0)
            exit()
    print(pow(2,n//2,10**9+7))
else:
    a.append(0)
    a.sort()
    for i in range(n//2):
        if a[i*2]!=a[i*2+1] or a[i*2]!=i*2 or a[i*2+1]!=i*2:
            print(0)
            exit()
    print(pow(2,n//2,10**9+7))

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





if flag:print(2**(N//2)%MOD)
else:print(0)

Solution (Python):
from collections import Counter
mod = 1000000007
N = int(input())
A = list(map(int, input().split()))
A.sort()

if N % 2 != 0:  
    count = Counter(A)
    now_key = 2
    for k, v in count.items():
        if k == 0:
            if v != 1:
                print(0)
                exit()
        else:
            if k != now_key or v != 2:
                print(0)
                exit()
            now_key += 2
    print(2**(N//2) % mod)
else:  
    count = Counter(A)
    now_key = 1
    for k, v in count.items():
        if k != now_key or v != 2:
            print(0)
            exit()
        now_key += 2
    print(2**(N//2) % mod)

Solution (Python):
import sys
from collections import Counter
readline = sys.stdin.readline
N = int(readline())
A = list(map(int, readline().split()))
MOD = 10**9+7
CA = Counter(A)
ans = 0
if N % 2 == 0:
    if all(CA[2*i+1] == 2 for i in range(N//2)):
        ans = pow(2, N//2, MOD)
else:
    if CA[0] == 1 and all(CA[2*i+2] == 2 for i in range(N//2)):
        ans = pow(2, N//2, MOD)
print(ans)

Solution (Python):
import sys
input = sys.stdin.readline
from operator import itemgetter
sys.setrecursionlimit(10000000)
INF = 10**30
from collections import Counter
from math import factorial

def main():
    n = int(input().strip())
    v = list(map(int, input().strip().split()))
    l = [0] * n
    for i in range(n):
        l[i] = abs(n-2*i-1)
    if sorted(v) != sorted(l):
        print(0)
        return
    c = dict(Counter(l))
    ans = 1
    d = 10**9 + 7
    for v in c.values():
        ans *= factorial(v) % d
    print(ans % d)

if __name__ == '__main__':
    main()

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

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
l = [0]* n
for a_ in a:
    l[a_] += 1
mod = 10 ** 9 + 7
if n % 2 == 1:
    if l[0] == 1 and l[2::2] == [2] * (n // 2):
        print(2 ** (n // 2) % mod)
    else:
        print(0)
else:
    if l[1::2] == [2] * (n // 2):
        print(2 ** (n // 2) % mod)
    else:
        print(0)

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

a.sort()

if a[0] == 0:
    ans = True
    for i in range(n):
        if a[i] != ((i+1)//2)*2:
            ans = False
            break
    if ans:
        print(2**(n//2) % (10**9+7))
    else:
        print(0)
else:
    ans = True
    for i in range(n):
        if a[i] != (i//2)*2+1:
            ans = False
            break
    if ans:
        print(2**(n//2) % (10**9+7))
    else:
        print(0)

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

Solution (Python):
from collections import Counter
n=int(input())
al=list(map(int,input().split()))
mod=10**9+7
cl=Counter(al)
if n%2==0:
    for i in range(1,n,2):
        if cl[i]!=2:
            print(0)
            break
    else:
        print(2**(n//2)%mod)
else:
    if cl[0]!=1:
        print(0)
        exit()
    for i in range(2,n,2):
        if cl[i]!=2:
            print(0)
            break
    else:
        print(2**(n//2)%mod)

Solution (Python):
from collections import Counter

N=int(input())
C=Counter(list(map(int,input().split())))

f=True
if N%2==0:
    for i in range(1,N+1,2):
        if C[i]!=2:
            f=False
            ans=0
            break
    if f:
        ans=(2**(N//2))%(10**9+7)
elif N%2==1:
    if C[0]!=1:
        f=False
        ans=0
    else:
        for i in range(2,N+1,2):
            if C[i]!=2:
                f=False
                ans=0
                break
    if f:
        ans=(2**((N-1)//2))%(10**9+7)

print(ans)

Solution (Python):
def main():
    mod=10**9+7
    n=int(input())
    a = list(map(int,input().split()))
    a.sort()
    if n%2==0:
        check=[]
        for i in range(n//2):
            check.append(i*2+1)
            check.append(i*2+1)
        if a!=check:
            print(0)
            return
        ans=1
        for _ in range(n//2):
            ans=(ans*2)%mod
        print(ans)
    else:
        check=[0]
        for i in range(n//2):
            check.append((i+1)*2)
            check.append((i+1)*2)
        if a!=check:
            print(0)
            return
        ans=1
        for _ in range(n//2):
            ans=(ans*2)%mod
        print(ans)

if __name__ == "__main__":
    main()

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

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

check = True
A = sorted(A)
if N % 2 == 0:
    for i in range(N):
        if i % 2 == 0 and A[i] != i + 1:
            check = False
        if i % 2 == 1 and A[i] != i:
            check = False

if N % 2 != 0:
    for i in range(N):
        if i % 2 == 0 and A[i] != i:
            check = False
        if i % 2 == 1 and A[i] != i + 1:
            check = False

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

Solution (Python):
def solve() -> int:
    from collections import defaultdict

    mod = 10 ** 9 + 7

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

    d = defaultdict(int)

    for a_ in a:
        d[a_] += 1
        if d[a_] > 2:
            return 0

    q, r = divmod(n, 2)
    if r == 1:
        if d[0] != 1:
            return 0
        cur = 2
        while cur < n:
            if d[cur] != 2:
                return 0
            cur += 2
        return (1 << q) % mod
    else:
        cur = 1
        while cur < n:
            if d[cur] != 2:
                return 0
            cur += 2
        return (1 << q) % mod


if __name__ == '__main__':
    print(solve())

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

for i in range(N):
  if A[i]==N-2*(i//2)-1:
    pass
  else:
    print(0)
    exit()
    
print((2**(N//2))%mod)

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

A.sort()
flag = True
for i in range(N):
  if N%2 == 0:
    if A[i] != (i//2)*2+1:
      flag = False
      break
  else:
    if A[i] != ((i+1)//2)*2:
      flag = False
      break
print(2**(N//2) % MOD if flag else 0)

Solution (Python):


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


if N%2==1:
    if A[0]!=0:
        print(0)
        exit()
    for i in range(1,N)[::2]:
        if A[i]==-int(-i//2)*2 and A[i+1]==-int(-i//2)*2:
            pass
        else:
            print(0)
            exit()
    print(2**(N//2)%(10**9+7))
else:
    for i in range(N)[::2]:
        if A[i]==-int(-i//2)*2+1 and A[i+1]==-int(-i//2)*2+1:
            pass
        else:
            print(0)
            exit()
    print(2**(N//2)%(10**9+7))

Solution (Python):
def main():
    N = int(input())
    A = [int(i) for i in input().split()]
    MOD = 10**9 + 7
    from collections import Counter
    A_c = Counter(A)
    for k,v in A_c.items():
        if k == 0 and v != 1:
            return print(0)
        elif k != 0 and v != 2:
            return print(0)
    else:
        print(2 ** (N//2) % MOD)
if __name__ == '__main__':
    main()

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

def main():
    N = int(input())
    A = list(map(int, input().split()))
    A.sort()
    for i in range(N):
        if len(A)%2 == 0: 
            if A[i] != 1 + i//2*2:
                print(0)
                return
        else: 
            if A[i] != (i+1)//2*2:
                print(0)
                return
    ans = 1
    for _ in range(N//2):
        ans *= 2
        ans %= 10**9+7
    print(ans)

if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter

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

cntA = Counter(A)

if N % 2 == 0:
    for i in range(1, N, 2):
        if cntA[i] != 2:
            print(0)
            exit()
        cntA[i] = 0
    if max(cntA.values()) > 0:
        print(0)
        exit()
    print(pow(2, N // 2, MOD))
else:
    for i in range(2, N, 2):
        if cntA[i] != 2:
            print(0)
            exit()
        cntA[i] = 0
    if cntA[0] != 1:
        print(0)
        exit()
    cntA[0] = 0
    if max(cntA.values()) > 0:
        print(0)
        exit()
    print(pow(2, N // 2, MOD))