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()))
l=[0]*n
for i in range(n):
    l[a[i]]+=1

if n%2==1:
    if l[0]!=1:
        print(0)
        exit()
ans=1
for i in range(n):
    if n%2==0:
        if i%2==0:
            if l[i]!=0:
                print(0)
                exit()
    else:
        if i%2==1:
            if l[i]!=0:
                print(0)
                exit()
    
    if l[i]==2:
        ans*=2
    elif l[i]>2:
        print(0)
        exit()
    ans%=(10**9 +7)
print(ans)

Solution (Python):
import sys
import heapq, math
from itertools import zip_longest, permutations, combinations, combinations_with_replacement
from itertools import accumulate, dropwhile, takewhile, groupby
from functools import lru_cache
from copy import deepcopy

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

B = [0] * N

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

ok = True

if N % 2 == 1:
    ok = ok and B[0] == 1
    for i in range(1, N):
        ok = ok and B[i] == (2 if i % 2 == 0 else 0)
else:
    for i in range(N):
        ok = ok and B[i] == (0 if i % 2 == 0 else 2)

ans = 1
MOD = int(1e9) + 7
for _ in range(N // 2):
    ans *= 2
    ans %= MOD

print(ans if ok else 0)

Solution (Python):
n = int(input())
a_list = sorted([int(x) for x in input().split()], reverse=True)
m = n
if m % 2 == 1:
    a_list.append(0)
    m += 1
for i in range(0, m, 2):
    if not (a_list[i] == a_list[i + 1] == n - (i + 1)):
        print(0)
        exit()
print(2 ** (n // 2) % (10 ** 9 + 7))

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

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

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

if n%2 == 0: 
  for i in range(0,n,2):
    if a[i] != i+1 or a[i] != a[i+1]:
      print(0)
      exit()
else: 
  if a[0] != 0: 
    print(0)
    exit()
  else:
    for i in range(1,n,2):
      if a[i] != i+1 or a[i] != a[i+1]:
        print(0)
        exit()

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

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

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

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

mod = 10 ** 9 + 7

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

res = 1

if n % 2 == 1:
    if cnt[0] != 1:
        print(0)
        exit()
    
    for i in range(1, n):
        if i % 2 == 1:
            if cnt[i] > 0:
                print(0)
                exit()
        else:
            if cnt[i] == 2:
                res = res * 2 % mod
            else:
                print(0)
                exit()
    
else:
    for i in range(1, n):
        if i % 2 == 0:
            if cnt[i] > 0:
                print(0)
                exit()
        else:
            if cnt[i] == 2:
                res = res * 2 % mod
            else:
                print(0)
                exit()

print(res)

Solution (Python):
from collections import Counter
n=int(input())
a=sorted(list(map(int,input().split())))
a_count=Counter(a)
if n%2==1:
    ans=1
    for i in a_count:
        if i%2!=0:
            print(0)
            break
        else:
            if i==0:
                if a_count[i]!=1:
                    print(0)
                    break
            
            else:
                if a_count[i]==2:
                     ans=(ans*2)%(10**9+7)
                else:
                    print(0)
                    break
    else:
      print(ans)
else:
    ans=1
    for j in a_count:
        if j%2!=1:
            print(0)
            break
        else:
            if a_count[j]==2:
                ans=(ans*2)%(10**9+7)
           
            else:
                print(0)
                break
    else:
      print(ans)

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

A = sorted(A)
ans = 1
if N % 2 == 0:
  for i in range(N):
    xx = int(i / 2)
    if A[i] != 2 * xx + 1:
      ans = 0
    else:
      if i % 2 == 1:
        ans *= 2
        ans %= mod
else:
  for i in range(N):
    xx = int((i + 1)/2)
    if A[i] != 2 * xx:
      ans = 0
    else:
      if (i % 2 == 0) and (i != 0):
        ans *= 2
        ans %= mod
      
      
  
  
print(ans)

Solution (Python):
n=int(input())
a=[int(i) for i in input().split()]

def somosomo(a):
    ans=[]
    if n%2==1:
        ans.append(0)
        for i in range(1,n//2+1):
            ans.append(i*2)
            ans.append(i*2)
        b=sorted(a)
        if b==ans:
            return True
        return False
    else:
        for i in range(1,n//2+1):
            ans.append(i*2-1)
            ans.append(i*2-1)
        b=sorted(a)
        if b==ans:
            return True
        return False

def two_ride(n):
    ans=1
    for i in range(n):
        ans*=2
        ans%=10**9+7
    return ans

if somosomo(a):
    print(two_ride(n//2))
else:
    print(0)

Solution (Python):
import sys
import math
import itertools
import bisect
from copy import copy,deepcopy
from collections import deque,Counter
from decimal import Decimal
def s(): return input()
def i(): return int(input())
def S(): return input().split()
def I(): return map(int,input().split())
def L(): return list(map(int,input().split()))
def l(): return list(map(int,input().split()))
def lcm(a,b): return a*b//math.gcd(a,b)
sys.setrecursionlimit(10 ** 9)
INF = 10**9
mod = 10**9+7

N = i()
A = l()
ans = 1
l = [0]*N
for i in range(N):
    l[A[i]] += 1
for i in range(N):
    c = l[i]
    if N%2 == i%2:
        if c:
            ans *= 0
    else:
        if c == 0:
            ans *= 0
        if c == 1:
            if i != 0:
                ans *= 0
        if c == 2:
            ans *= 2
print(ans%mod)

Solution (Python):
from collections import Counter

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

c=Counter(a)
ans=1
if n%2==1:
    for i in range(n):
        if i%2==1 and c[i]>0:
            ans=0
            break
        elif i%2==0 and c[i]==2:
            ans*=2
            ans%=1000000007
        if i==0 and c[i]!=1:
            ans=0
            break
else:
    for i in range(n):
        if i%2==0 and c[i]>0:
            ans=0
            break
        elif i%2==1 and c[i]==2:
            ans*=2
            ans%=1000000007
print(ans)

Solution (Python):
import sys



n = int(input())

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

record = {}

possible = True


for e in a:
    if(e in record.keys()):
        record[e] += 1
        if(record[e] == 2):
            if(e == 0):
                possible = False
                break
        if(record[e] == 3):
            possible = False
            break
    else:
        record[e] = 1

if(possible == False):
    print(0)
    sys.exit()

multiCount = int(n / 2)

print(2 ** multiCount % (10 ** 9 + 7))

Solution (Python):
n = int(input())
arr = list(map(int , input().split()))
mod = 10**9+7
h = [0 for i in range(0,n)]
for i in range(0,n):
	h[arr[i]]=h[arr[i]]+1
	if n%2==0 and arr[i]==0:
		print(0)
		exit()
ans=1
if n%2:
	for i in range(2 ,n, 2):
		if h[i]!=2:
			print(0)
			exit()
		ans = (ans*2)%mod
else:
	for i in range(1, n , 2):
		if h[i]!=2:
			print(0)
			exit()
		ans = (ans*2)%mod
print(ans)

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

a.sort()

if n%2 == 1: 
    if a[0] != 0:
        print(0)
        exit()
    else:
        a.remove(0)
        tmp = 2
else:
    tmp = 1

for i in range(n//2):
    if tmp == a[0] and tmp == a[1]:
        a.remove(tmp)
        a.remove(tmp)
    else:
        print(0)
        exit()
    tmp += 2

if len(a) == 0:
    print((2**(n//2))%mod)
else:
    print(0)

Solution (Python):
n=int(input())
lst=list(map(int,input().split()))
if n%2==0:
    cnt=[0]*n
    for i in range(n):
        p=lst[i]
        if p%2==0:
            print(0)
            exit()
        cnt[p]+=1
        if cnt[p]>=3:
            print(0)
            exit()
    print(pow(2,n//2,10**9+7))
else:
    cnt=[0]*n
    for i in range(n):
        p=lst[i]
        if p%2==1:
            print(0)
            exit()
        cnt[p]+=1
        if p==0:
            if cnt[0]>=2:
                print(0)
                exit()
        else:
            if cnt[p]>=3:
                print(0)
                exit()
    print(pow(2,n//2,10**9+7))

Solution (Python):
import sys

read = sys.stdin.read
readline = sys.stdin.readline
readlines = sys.stdin.readlines
sys.setrecursionlimit(10 ** 9)
INF = 1 << 60
MOD = 1000000007


def main():
    N, *A = map(int, read().split())

    A.sort()

    ok = True
    if len(A) % 2 == 0:
        for i in range(N // 2):
            if not A[2 * i] == A[2 * i + 1] == 2 * i + 1:
                ok = False
                break
    else:
        if A[0] != 0:
            ok = False
        else:
            for i in range(N // 2):
                if not A[2 * i + 1] == A[2 * i + 2] == 2 * i + 2:
                    ok = False
                    break

    if ok:
        ans = pow(2, N // 2, MOD)
    else:
        ans = 0

    print(ans)

    return


if __name__ == '__main__':
    main()

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

A.sort()
check=[0]*N

for idx in range(N%2,N,2):
    check[idx]=idx+1
    check[idx+1]=idx+1

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

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

check=[0]*N

for idx in range(N%2,N,2):
    check[idx]=idx+1
    check[idx+1]=idx+1

ans=0

if check == A:
    if N % 2 == 0:
        ans=(2**(N//2))%(10**9+7)
    elif N % 2 != 0:
        ans=(2**((N-1)//2))%(10**9+7)
    
print(ans)

Solution (Python):
import sys
import itertools

import time
import math
import heapq
from collections import defaultdict
sys.setrecursionlimit(10 ** 7)
 
INF = 10 ** 18
MOD = 10 ** 9 + 7
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines



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

X = [0] * N
for i, a in enumerate(A):
    j = (N - 1 - a) // 2
    X[j] += 1

for i, x in enumerate(X):
    if x == 1 and not (i == (N + 1) // 2 - 1):
        print(0)
        exit()
    if x > 2:
        print(0)
        exit()

ans = 1
for x in X:
    if x == 0:
        break
    ans *= x
    ans %= MOD
print(ans)

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
flg = 0

a.sort()
if n % 2 == 0:
  if a[0] == 1 and a[1] == 1:
    for i in range(2, n, 2):
      if a[i] == a[i + 1] and a[i - 1] + 2 == a[i]:
        continue
      else:
        flg = 1
        break
  else:
    flg = 1
else:
  if a[0] == 0:
    for i in range(1, n, 2):
      if a[i] == a[i + 1] and a[i - 1] + 2 == a[i]:
        continue
      else:
        flg = 1
        break
  else:
    flg = 1

if flg == 1:
  print(0)
else:
  print((2 ** (n // 2)) % (10 ** 9 + 7))

Solution (Python):
import bisect, collections, copy, heapq, itertools, math, string, sys
input = lambda: sys.stdin.readline().rstrip() 
sys.setrecursionlimit(10**7)
INF = float('inf')
MOD = 10 ** 9 + 7
def I(): return int(input())
def F(): return float(input())
def SS(): return input()
def LI(): return [int(x) for x in input().split()]
def LI_(): return [int(x)-1 for x in input().split()]
def LF(): return [float(x) for x in input().split()]
def LSS(): return input().split()

def resolve():
    N = I()
    A = LI()

    if N % 2 == 0:
        if sorted(A) == [i // 2 * 2 + 1 for i in range(N)]:
            print(pow(2, N // 2, MOD))
        else:
            print(0)
    else:
        if sorted(A) == [(i // 2 + 1) * 2 for i in range(-1, N - 1)]:
            print(pow(2, (N - 1) // 2, MOD))
        else:
            print(0)

if __name__ == '__main__':
    resolve()

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

if N%2==0:
  B = [1+2*(n//2) for n in range(N)]
else:
  B = [2*(n//2) for n in range(1,1+N)]

if A==B:
  print(pow(2,N//2,10**9+7))
else:
  print(0)

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

if N%2==0:
  B = [2*(n//2)+1 for n in range(N)]
else:
  B = [2*(n//2) for n in range(1,N+1)]

if A==B:
  print(pow(2,N//2,10**9+7))
else:
  print(0)

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

d = [0]*(n+1)
for x in a:
    d[x] += 1
ans = 1
if n%2 == 0:
    sw = 1
    for i,x in enumerate(d):
        if i%2 != 0:
            if x == 2:
                ans *= 2
                ans %= mod
            else:
                sw = 0
                break
        else:
            if x != 0:
                sw = 0
                break
else:
    sw = 1
    for i,x in enumerate(d):
        if i%2 == 0:
            if i == 0:
                if x != 1:
                    sw = 0
                    break
            else:
                if x == 2:
                    ans *= 2
                    ans %= mod
                else:
                    sw = 0
                    break
        else:
            if x != 0:
                sw = 0
                break
if sw == 0:
    ans = 0
print(ans)

Solution (Python):
import sys
from collections import deque
p=10**9+7

def main(n,a):
  h=n//2
  g=n%2
  a.sort()
  c=[2*(x//2)+g+1 for x in range(n-g)]
  if g==1:
    c.insert(0,0)
  if a!=c:
      return 0
  return 2**(h%(p-1)) % p

if __name__=='__main__':
  n=int(input())
  a=list(map(int,sys.stdin.readline().strip().split()))
  print(main(n,a))

Solution (Python):
import math

N = 5
ARR = [2, 4, 4, 0, 2]

N = 7
ARR = [6, 4, 0, 2, 4, 0, 2]




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


def calculate(n, arr):
    if n % 2 == 0:
        n = n // 2
        start = 1
        finalResult = pow(2, n, 1000000000 + 7)
    else:
        n = n // 2 + 1
        start = 0
        finalResult = pow(2, (n - 1), 1000000000 + 7)

    result = {}
    for i in range(n):
        index = start + 2 * i
        if index == 0:
            result.__setitem__(0, 1)
        else:
            result.__setitem__(index, 2)

    isOk = True
    for i in range(len(arr)):
        if result.get(arr[i]) == None:
            isOk = False
            break

        if result.get(arr[i]) == 0:
            isOk = False
            break

        result.__setitem__(arr[i], result.get(arr[i])-1)

    if isOk == False:
        print(0)
        return

    if sum(result.values()) == 0:
        print(finalResult)
    else:
        print(0)


calculate(N, ARR)

Solution (Python):
MOD = 10 ** 9 + 7
num = [0] * (10 ** 5 + 1)
N = int(input())
A = list(map(int,input().split()))
for i in range(len(A)):
	num[A[i]] += 1
if N % 2 == 1:
	for i in range(0,N,2):
		cnt = num[i]
		if i == 0:
			if cnt != 1:
				print(0)
				exit()
		else:
			if cnt != 2:
				print(0)
				exit()
	print(2 ** (N // 2) % MOD)
else:
	for i in range(1,N,2):
		cnt = num[i]
		if cnt != 2:
			print(0)
			exit()
	print(2 ** (N // 2) % MOD)

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

a.sort()

if n % 2 == 0:
    for i in range(n):
        if i % 2 == 0:
            if a[i] != i + 1:
                print(0)
                exit()
        else:
            if a[i] != i:
                print(0)
                exit()
    print(pow(2, n//2, mod))

else:
    for i in range(n):
        if i % 2 == 0:
            if a[i] != i:
                print(0)
                exit()
        else:
            if a[i] != i + 1:
                print(0)
                exit()
    print(pow(2, n//2, mod))

Solution (Python):
n = int(input())
a = sorted(list(map(int, input().split())))
ans = 1

if n%2 == 0:
    for i in range(0, n, 2):
        if a[i] != i + 1 or a[i + 1] != i + 1:
            print(0)
            exit()
else:
    if a[0] != 0:
        print(0)
        exit()
    for i in range(1, n, 2):
        if a[i] != i + 1 or a[i + 1] != i + 1:
            print(0)
            exit()

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

print(ans)

Solution (Python):
def main():
  N=int(input())
  A=list(map(int,input().split()))
  mod=10**9+7
  ans=1
  A.sort()
  if N%2==0:
    for i in range(0,N,2):
      if A[i]!=A[i+1] or A[i]!=i+1:
        print(0)
        exit()
      ans=ans*2%mod
    print(ans)
  else:
    if A[0]!=0:
      print(0)
      exit()
    ans=1
    for i in range(1,N,2):
      if A[i]!=A[i+1] or A[i]!=i+1:
        print(0)
        exit()
      ans=ans*2%mod
    print(ans)
if __name__=='__main__':
  main()

Solution (Python):
import sys, os, math, bisect, itertools, collections, heapq, queue

from decimal import Decimal
from collections import defaultdict, deque

sys.setrecursionlimit(10000000)

ii = lambda: int(sys.stdin.buffer.readline().rstrip())
il = lambda: list(map(int, sys.stdin.buffer.readline().split()))
fl = lambda: list(map(float, sys.stdin.buffer.readline().split()))
iln = lambda n: [int(sys.stdin.buffer.readline().rstrip()) for _ in range(n)]

iss = lambda: sys.stdin.buffer.readline().decode().rstrip()
sl = lambda: list(map(str, sys.stdin.buffer.readline().decode().split()))
isn = lambda n: [sys.stdin.buffer.readline().decode().rstrip() for _ in range(n)]

lcm = lambda x, y: (x * y) // math.gcd(x, y)

MOD = 10 ** 9 + 7
MAX = float('inf')


def main():
    if os.getenv("LOCAL"):
        sys.stdin = open("input.txt", "r")

    N = ii()
    A = il()
    cnt = collections.Counter(A)

    start = 1 if N % 2 == 0 else 0
    m = 0
    for n in range(start, N, 2):
        if n == 0 and cnt[n] == 1:
            continue
        elif cnt[n] == 2:
            m += 1
            continue
        else:
            print(0)
            exit()
    print((2**m)%MOD)


if __name__ == '__main__':
    main()

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

ans = 0
A_test = sorted(list(set(A)))

if N % 2 == 1:
    judge = [i for i in range(0,N,2)]
    if (A_test == judge) and (A.count(0) == 1):
        ans = 2**(N//2)
else:
    judge = [i for i in range(1,N,2)]
    if A_test == judge:
        ans = 2**(N//2)

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

Solution (Python):
N=int(input())
S=list(map(int,input().split()))
lenS=len(S)
T=[]
for i in range(1,N+1):
    T.append(abs(i-(N+1-i)))

T.sort()
S.sort()



for i in range(N):
    if T[i]!=S[i]:
        print(0)
        exit()


ans=1
nagasa=lenS//2
for i in range(nagasa):
    
    ans=(ans*2)%(10**9+7)

print(ans)

Solution (Python):
from collections import Counter

N,*A = map(int, open(0).read().split())
ac = Counter(A)
if N % 2 == 0:
    for i in range(1,N,2):
        if ac[i] != 2:
            print(0)
            break
    else:
        print(pow(2,N//2,1000000007))
else:
    if ac[0] != 1:
        print(0)
    else:
        for i in range(2,N,2):
            if ac[i] != 2:
                print(0)
                break
        else:
            print(pow(2,N//2,1000000007))

Solution (Python):
import sys
import numpy as np
import random
from decimal import Decimal
import itertools
import re
import bisect
from collections import deque, Counter
from functools import lru_cache

sys.setrecursionlimit(10**9)
INF = 10**13
def LI(): return list(map(int, sys.stdin.buffer.readline().split()))
def I(): return int(sys.stdin.buffer.readline())
def LS(): return sys.stdin.buffer.readline().rstrip().decode('utf-8').split()
def S(): return sys.stdin.buffer.readline().rstrip().decode('utf-8')
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
def SERIES(n): return np.fromstring(sys.stdin.buffer.read(), dtype=np.int32, sep=' ')
def GRID(h,w): return np.fromstring(sys.stdin.buffer.read(), dtype=np.int32, sep=' ').reshape(h,-1)[:,:w]
def GRIDfromString(h,w): return np.frombuffer(sys.stdin.buffer.read(), 'S1').reshape(h,-1)[:,:w]
MOD = 1000000007

def main():
	n = I()
	a_list = LI()
	a_dict = list(Counter(a_list).items())
	a_dict.sort()
	ans = 1
	if n % 2 == 0:
		for i in range(len(a_dict)):
			diff, number = a_dict[i]
			if diff % 2 == 0:
				ans = 0
				break
			if diff != 2*i+1 or number != 2:
				ans = 0
				break
			ans *= 2
			ans %= MOD
	else:
		for i in range(len(a_dict)):
			diff, number = a_dict[i]
			if diff % 2 == 1 or (diff == 0 and number !=1):
				ans = 0
				break
			if diff != 2*i or (diff > 0 and number != 2):
				ans = 0
				break
			if diff != 0:
				ans *= 2
				ans %= MOD
	print(int(ans))


	


if __name__ == '__main__':
    main()

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

N = int(input())
A = list(map(int,input().split()))
m = 1000000007

flag0 = 1
count = 0

if N %2 ==0:
    colA = collections.Counter(A)
    for key,val in colA.items():
        if key%2 != 1 or val != 2:
            flag0 = 0
            break
    for i in range(1,N,2):
        if i not in colA.keys():
            flag = 0
            break
        else:
            count +=1

else:
    A.append(0)
    colA = collections.Counter(A)
    for key,val in colA.items():
        if key%2 != 0 or val != 2:
            flag0 = 0
            break
    for i in range(0,N,2):
        if i not in colA.keys():
            flag = 0
            break
        else:
            count +=1
    count -=1


print(((2**count)%m)*flag0)

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

niseven = (n%2 == 0)

cd = dict()
for a in (A):
    cd.setdefault(a, 0)
    cd[a] += 1
    if a == 0 and cd[a] > 1:
        print(0)
        break
    if a > 0 and cd[a] > 2:
        print(0)
        break
    if (a%2==0) == niseven:
        print(0)
        break
else:
    print(pow(2, n//2, mod))

Solution (Python):
import sys, os, math, bisect, itertools, collections, heapq, queue

from decimal import Decimal
from collections import defaultdict, deque



sys.setrecursionlimit(10000000)

ii = lambda: int(sys.stdin.buffer.readline().rstrip())
il = lambda: list(map(int, sys.stdin.buffer.readline().split()))
fl = lambda: list(map(float, sys.stdin.buffer.readline().split()))
iln = lambda n: [int(sys.stdin.buffer.readline().rstrip()) for _ in range(n)]

iss = lambda: sys.stdin.buffer.readline().decode().rstrip()
sl = lambda: list(map(str, sys.stdin.buffer.readline().decode().split()))
isn = lambda n: [sys.stdin.buffer.readline().decode().rstrip() for _ in range(n)]

lcm = lambda x, y: (x * y) // math.gcd(x, y)


MOD = 10 ** 9 + 7
MAX = float('inf')


def main():
    if os.getenv("LOCAL"):
        sys.stdin = open("input.txt", "r")

    N = ii()
    A = il()
    cnt = collections.Counter(A)

    for k, v in cnt.items():
        if k == 0 and v != 1:
            print(0)
            exit()
        elif k != 0 and v != 2:
            print(0)
            exit()
    print((2 ** (N // 2))%MOD)


if __name__ == '__main__':
    main()

Solution (Python):
import sys

readline = sys.stdin.readline
MOD = 10 ** 9 + 7
INF = float('INF')
sys.setrecursionlimit(10 ** 5)


def main():
    from collections import Counter

    n = int(readline())
    a = list(map(int, readline().split()))
    counter = Counter(a)
    ok = True

    if n % 2 == 1:
        if counter[0] != 1:
            ok = False

        for i in range(2, n, 2):
            if counter[i] != 2:
                ok = False
    else:
        for i in range(1, n, 2):
            if counter[i] != 2:
                ok = False

    if ok:
        print(pow(2, n // 2, MOD))
    else:
        print(0)


if __name__ == '__main__':
    main()

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

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

if len(a)%2==1:
    tmp = [0]
    for i in range((len(a)-1)//2):
        tmp.append((i+1)*2)
        tmp.append((i+1)*2)
    if a == tmp:
        ans = (2**((len(a)-1)//2))%(10**9+7)
    else:
        ans = 0
else:
    tmp = []
    for i in range(len(a)//2):
        tmp.append(2*i+1)
        tmp.append(2*i+1)
    if a == tmp:
        ans = (2**(len(a)//2))%(10**9+7)
    else:
        ans = 0
print(ans)

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

Solution (Python):
from collections import Counter

N = int(input())
A = list(map(int, input().split()))
MOD = int(1e9) + 7


if N % 2 == 0:
    c = Counter(A)
    if all(i == 2 for i in c.values()):
        print(pow(2, N//2, MOD))
    else:
        print(0)

else:
    A.sort()
    A = A[1:]
    c = Counter(A)
    if all(i == 2 for i in c.values()):
        print(pow(2, N//2, MOD))
    else:
        print(0)

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

m = 1000000007

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 %= m
    print(result)

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

C = Counter(A)
C = sorted(C.items(), key=lambda x: x[0])
if N % 2 == 0:
    s = 1
    for k, v in C:
        if k != s or v != 2:
            print(0)
            sys.exit()
        s += 2
    print(pow(2, (N // 2), MOD))
else:
    s = 0
    for k, v in C:
        if k == 0:
            if k != 0 or v != 1:
                print(0)
                sys.exit()
            s += 2
            continue
        if k != s or v != 2:
            print(0)
            sys.exit()
        s += 2
    print(pow(2, (N - 1) // 2, MOD))

Solution (Python):
import sys
from collections import Counter

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

l = []

for i in range(n):
    li = abs(i - (n-1-i))
    l.append(li)
    
l.sort()


for ai, li in zip(l,a):
    if ai != li:
        print(0)
        sys.exit()

d = Counter(l)
mod = 10 ** 9 + 7
ans = 1

for li in d:
    for j in range(1,d[li]+1):
        ans *= j
        ans %= mod

print(ans)

Solution (Python):
MOD = 10**9+7


def read_int():
    return int(input().strip())


def read_ints():
    return list(map(int, input().strip().split(' ')))


def pow(b, p):
    ans = 1
    for _ in range(p):
        ans = (ans*b)%MOD
    return ans


def solve():
    """
    if N is odd, 
    N-1 : 2
    N-3 : 2
    0   : 1
    if N is even,
    N-1 : 2
    N-3 : 2
    1   : 1


    1 2 3 4 5 6
    1 2 3 4 5
    """
    N = read_int()
    A = read_ints()
    D = [0]*((N+1)//2)
    if N%2 == 0:
        for a in A:
            if a%2 == 0:
                return 0
            if a >= N:
                return 0
            if D[a//2] == 2:
                return 0
            D[a//2] += 1
    else:
        for a in A:
            if a%2 == 1:
                return 0
            if a >= N:
                return 0
            if D[a//2] == 2:
                return 0
            if D[0] == 2:
                return 0
            D[a//2] += 1
    return pow(2, N//2)


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

Solution (Python):
N = int(input())
count = [0]*(N+1)
modz = 10**9 + 7

def junretsu(a):
    if a <= 0: return 1
    if (a & 0x01) == 1:
        return 2*junretsu(a-1) % modz
    else:
        rr = junretsu(a>>1)
        return rr*rr % modz

pos = list(map(int, input().split()))
for i in range(N):
    count[pos[i]] += 1

diff = [0]*(N+1)
for i in range(1, N+1):
    d = abs((N - i) - (i-1))
    diff[d] += 1

invalid = False
total = 1
for i in range(N):
    if count[i] != diff[i]:
        invalid = True
        break

if invalid:
    print(0)
else:
    print(junretsu(int(N/2)))

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

m = 1000000007

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 %= m
    print(result)

Solution (Python):
n = int(input())
ls = list(map(int,input().split()))
ls.sort()
if n % 2 == 0:
    if ls[::2] == ls[1::2] and ls[::2] == [e for e in range(n) if e % 2 != 0]:
        print(2**(int(n/2))%(10**9+7))
    else:
        print(0)
else:
    if ls[1::2] == ls[2::2] and ls[::2] ==  [e for e in range(n) if e % 2 == 0]:
        print(2**(int(n/2))%(10**9+7))
    else:
        print(0)

Solution (Python):
from collections import Counter


def mod_pow(a, n, mod):
    """
    二分累乗法による a^n (mod m)の実装
    :param a: 累乗の底
    :param n: 累乗の指数
    :param mod: 法
    :return: a^n (mod m)
    """

    result = 1
    a_n = a
    while n > 0:
        if n & 1:
            result = result * a_n % mod
        a_n = a_n * a_n % mod
        n >>= 1
    return result


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

if A[0] > 1:
    print(0)
elif sum([key for key, value in A.items() if value == 1]) != 0:
    print(0)
else:
    print(mod_pow(2, N // 2, MOD))