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):
def index(n:int, a: int):
    if a % 2 == 0:
        i = n // 2 - a // 2
        j = (i + 1) * -1
        return (i, j) if i != n // 2 else (i,)
    else:
        i = (n // 2 - 1) - (a - 1) // 2
        j = (i + 1) * -1
        return (i, j)

n = int(input())
line = [0 for _ in range(n)]
for a in map(int, input().split()):
    for i in index(n, a):
        line[i] += 1
else:
    if n == 1 and line == [1]:
        print(1)
    elif n % 2 == 0 and set(line) == {2}:
        print(2 ** (n // 2) % (10 ** 9 + 7))
    elif n % 2 == 1 and set(line) == {1, 2} and line[n//2] == 1:
        print(2 ** ((n - 1) // 2) % (10 ** 9 + 7))
    else:
        print(0)

Solution (Python):
n = int(input())
a = [int(x) for x in input().split()]
line = [abs(i - (n - i- 1)) for i in range(n)]
if sorted(a) == sorted(line):
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    print(0)

Solution (Python):
n = int(input())
a = [int(x) for x in input().split()]
line = [abs(i - (n - i- 1)) for i in range(n)]
if sorted(a) == sorted(line):
    print((2 ** (n // 2)) %  (10 ** 9 + 7))
else:
    print(0)

Solution (Python):
from collections import*
N=int(input())
if N%2:
 if Counter(map(int,input().split()))==Counter(i//2*2for i in range(1,N+1)):print(2**(N//2)%(10**9+7))
 else:print(0)
else:
 if Counter(map(int,input().split()))==Counter(i//2*2+1for i in range(N)):print(2**(N//2)%(10**9+7))
 else:print(0)

Solution (Python):

import numpy as np

N = int(input())
A = np.array([int(x) for x in input().split()])
MOD = 10 ** 9 + 7

left = np.arange(N)
right = N-1-left
cnt_1 = np.bincount(np.abs(left-right))
cnt_2 = np.bincount(A)

if cnt_1.shape != cnt_2.shape or (cnt_1 != cnt_2).any():
    answer = 0
else:
    answer = pow(2, N//2, MOD)
print(answer)

Solution (Python):
MOD = 1000000007
import collections
N = int(input())
A = list(map(int, input().split()))
c = collections.Counter(A)

def chk(c, n):
    if n % 2:
        if 0 not in c or c[0] != 1:
            return False
        for i in range(2, (n//2)*2+1, 2):
            if i not in c or c[i] != 2:
                return False
    else:
        for i in range(1, n, 2):
            if i not in c or c[i] != 2:
                return False
    return True

if chk(c, N):
    ans = 2 ** (N//2) % MOD
else:
    ans = 0

print(ans)

Solution (Python):

import numpy as np
MOD = 10**9 + 7
N = int(input())
A = np.array([int(x) for x in input().split()])

left = np.arange(N)
right = N-1-left
cnt_1 = np.bincount(np.abs(left-right))
cnt_2 = np.bincount(A)

if cnt_1.shape != cnt_2.shape or (cnt_1 != cnt_2).any():
    answer = 0
else:
    answer = pow(2, N//2, MOD)

print(answer)

Solution (Python):
def pow2( n ):
    ans = 1 
    for i in range(n):
        ans = 2*ans % 1000000007
    return ans

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

if N % 2 == 0:
    flag = True
    for n in range(0,N-1,2):
        if AList[n] == n+1 and AList[n+1] == n+1:
            pass
        else:
            flag = False
            break

    if flag == False:
        print(0)
    else:
        a = N//2
        print(pow2(a))
else:
    flag = True
    if AList[0] != 0:
        flag = False
    else:
        for n in range(1,N-1,2):
            if AList[n] == n+1 and AList[n+1] == n+1:
                pass
            else:
                flag = False
                break
    if flag == False:
        print(0)
    else:
        a = N//2
        print(pow2(a))

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

if N%2==0:
  B = [2*(i//2)+1 for i in range(N)]
else:
  B = [2*(i//2) for i 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()))
flag=0
B=[0]*100000
mod=1000000007
if N%2==1:
    for i in range(N):
        B[A[i]]+=1
    for i in range(N):
        if i==0:
            if B[i]!=1:
                flag=1
        elif i%2==0:
            if B[i]!=2:
                flag=1

if N%2==0:
    for i in range(N):
        B[A[i]]+=1
    for i in range(N):
        if i%2==1:
            if B[i]!=2:
                flag=1


if flag==1:
    print(0)
else:
    print(2**(N//2)%mod)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
B = []
flag = 0

for i in range(N//2):
    B.append((N-1) - (i*2))
    B.append((N-1) - (i*2))
if N % 2 == 1:
    B.append(0)
        
A.sort()
B.sort()
if A == B:
    print((2**(N//2)) % (1000000007))
else:
    print(0)

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

if N % 2 == 0:
    for i in range(1, N, 2):
        B.append(i)
        B.append(i)
else:
    B.append(0)
    for i in range(2, N, 2):
        B.append(i)
        B.append(i)

if A != B:
    ans = 0
else:
    ans = 2 ** (N // 2) % mod

print(ans)

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

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

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
A.sort()
if N%2==1:
    l=[0]
    for i in range(2,N,2):
        l.append(i)
        l.append(i)
else:
    l=[1,1]
    for i in range(3,N,2):
        l.append(i)
        l.append(i)
if A==l:
    print(pow(2,N//2,10**9+7))
else:
    print(0)

Solution (Python):
import sys
from collections import Counter

stdin = sys.stdin
ni = lambda: int(ns())
na = lambda: list(map(int, stdin.readline().split()))
ns = lambda: stdin.readline()

mod = 10 ** 9 + 7

n = ni()
aaa = na()
c = Counter(aaa)
ct = 0
ans = 0
if n % 2 == 0:
    for k, v in c.items():
        if k % 2 != 1:
            ct = 0
            break
        if v == 2:
            ct += 1
        else:
            ct = 0
            break
else:
    for k, v in c.items():
        if k % 2 != 0:
            ct = 0
            break
        if k == 0:
            if v != 1:
                ct = 0
                break
        elif v == 2:
            ct += 1
        else:
            ct = 0
            break
if n == 1 and aaa[0] == 0:
    print(1)
elif ct == 0:
    print(0)
else:
    ans = 2 ** ct
    print(ans % mod)

Solution (Python):
def resolve():
    n=int(input())
    A=sorted(list(map(int,input().split())))
    if n%2:
        A.insert(0,0)
        flag=all(A[2*i]==2*i and A[2*i+1]==2*i for i in range(len(A)//2))
    else:
        flag=all(A[2*i]==2*i+1 and A[2*i+1]==2*i+1 for i in range(len(A)//2))
    print(2**(n//2)%(10**9+7) if flag else 0)
resolve()

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

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

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

dic= {}
for i in A:
    if i in dic:
        dic[i]+= 1
    else:
        dic[i] = 1

flag = 1

if N%2 == 1:
    for m, n in dic.items():
        if m == 0:
            if n != 1:
                flag = 0
                break
        elif m%2 == 1 or n != 2:
            flag = 0
            break
else:
    for m, n in dic.items():
        if m%2==0 or n != 2:
            flag = 0
            break
if flag:
    if N%2 == 0:
        print(2**(N//2)%1000000007)
    else:
        print(2**((N-1)//2)%1000000007)
else:
    print(0)

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

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

a.sort(reverse=True)
mod = 10**9+7
ans = 1

for i in range(n):
    
    if a[i] != n - 1 - 2*int(i*0.5):
        print(0)
        exit()
    elif i % 2 == 1:
        
        ans = ans * 2 % mod
        
        
print(ans)

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

if n%2 == 0:
  if 0 in A or len(set(A))!=n//2:
    flag = False
else:
  if A.count(0)!=1 or len(set(A))!=n//2+1:
    flag = False
if flag:
  print(2**(n//2) % mod)
else:
  print(0)

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

d = defaultdict(int)
for ai in a:
    d[ai] += 1

if n % 2 == 0:
    ans = 1
    for i in range(n//2):
        j = 2*i + 1
        ans *= 2 if d[j] == 2 else 0
        ans %= MOD
else:
    ans = 1 if d[0] == 1 else 0
    for i in range(n//2):
        j = 2 * (i+1)
        ans *= 2 if d[j] == 2 else 0
        ans %= MOD

print(ans)

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

Solution (Python):
N = int(input())
m = [2 * ((i - 1 + N % 2) // 2) + 1 - N % 2 for i in range(1, N + 1)]
for i, a in enumerate(sorted([int(a) for a in input().split()])):
  if m[i] != a:
    ret = 0
    break
else:
  ret = 2 ** (N // 2)

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

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

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

A = sorted([int(_) for _ in input().split()])
if N % 2 == 1:
    if A[0] != 0:
        print(0)
        exit()
    A.pop(0)
    s = 2
else:
    s = 1

ans = 1
MOD = 10 ** 9 + 7
for i in range(0, N // 2):
    v = s + 2 * i
    j = 2 * i
    
    if A[j] != v or A[j + 1] != v:
        print(0)
        exit()
    ans *= 2
    ans %= MOD

print(ans)

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

def solve(n,A):
    D=defaultdict(int)
    for a in A:
        D[a]+=1
    if n%2:
        if D[0]!=1:
            return 0
        for i in range(2,n,2):
            if D[i]!=2:
                return 0
    else:
        for i in range(1,n,2):
            if D[i]!=2:
                return 0
    return pow(2,n//2,mod)

print(solve(n,A))

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

Solution (Python):
import sys
input=sys.stdin.readline
N=int(input())
A=list(map(int,input().split()))
A.sort()
Devide_N=10**9+7
Rem_2_32_DN=(2**32)%Devide_N

if N%2==1:
  if (A[0]!=0 or A[1]==0 if N>2 else A[0]!=0):
    print(0)

  else:
    del A[0]
    for ch_n in range(1,(N-1)//2+1):
      if A[0]!=ch_n*2 or A[1]!=ch_n*2:
        break
      else:
        del A[0:2]
    else:
      exp=(N-1)//2
      
      exp_quotient_32=exp//32
      exp_rem_32=exp%32
      Rem_ans_Devide_N=1
      for _ in range(exp_quotient_32):
        Rem_ans_Devide_N=(Rem_ans_Devide_N*Rem_2_32_DN)%Devide_N
        
      print((Rem_ans_Devide_N*2**(exp_rem_32))%Devide_N)
      sys.exit()
    print(0)

else:
  for ch_n in range(1,N//2+1):
    if A[0]!=ch_n*2-1 or A[1]!=ch_n*2-1:
      break
    else:
      del A[0:2]
  else:
    exp=N//2
    
    exp_quotient_32=exp//32
    exp_rem_32=exp%32
    Rem_ans_Devide_N=1
    for _ in range(exp_quotient_32):
      Rem_ans_Devide_N=(Rem_ans_Devide_N*Rem_2_32_DN)%Devide_N
      
    print((Rem_ans_Devide_N*2**(exp_rem_32))%Devide_N)
    sys.exit()
  print(0)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
a.sort()
jun=1
if n%2==0:
  for i in range(n//2):
    if a[2*i] != 2*i+1 or a[2*i+1] != 2*i+1:
      print(0)
      exit()
    jun = jun*2%1000000007
  print(jun)
else:
  if n==1:
    if a[0]==0:
      print(1)
    else:
      print(0)
  else:
    for i in range(n//2):
      if a[2*i+1] != 2*(i+1) or a[2*i+2] != 2*(i+1):
        print(0)
        exit()
      jun = jun*2%1000000007
    print(jun)

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

l = len(a)
s = sorted(set(a))
if l % 2 == 0:
    if s == list(range(1, max(s)+1, 2)) and a.count(0) == 0:
        print(2 ** len(s) % (10 ** 9 + 7))
    else:
        print(0)
else:
    s = sorted(set(a))
    if s == list(range(0, max(s)+1, 2)) and a.count(0) == 1:
        print(2 ** (len(s)-1) % (10 ** 9 + 7))
    else:
        print(0)

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

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

ans = 1
for key, value in c.items():
    if key == 0:
        if n % 2 == 1 and value != 1:
            print(0)
            exit()
        else:
            continue
    elif value == 2:
        ans *= 2
        ans %= MOD
    else:
        print(0)
        exit()
print(ans)

Solution (Python):
n = int(input())
alist = list(map(int, input().split()))
len_alist = len(alist)

mod = 10**9 + 7

if len_alist % 2 == 0:
  nums = [2 for _ in range(n//2)]
  for a in alist:
    nums[(a-1)//2] -= 1
    if nums[(a-1)//2] < 0:
      break
  if all(num == 0 for num in nums):
    print(2**(n//2)%mod)
  else:
    print(0)
else:
  nums = [1] + [2 for _ in range((n-1)//2)]
  for a in alist:
    nums[(a)//2] -= 1
    if nums[(a)//2] < 0:
      break
  if all(num == 0 for num in nums):
    print(2**((n-1)//2)%mod)
  else:
    print(0)

Solution (Python):
from collections import Counter
n = int(input())
a = list(map(int, input().split()))
arr = [abs(i - (n-i-1)) for i in range(n)]
ans = (2**(n//2)) % (10**9 + 7) if Counter(a) == Counter(arr) else 0
print(ans)

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

Solution (Python):
def main():
    N = int(input())
    A = [int(a) for a in input().split()]
    div = pow(10, 9) + 7
    d = dict()
    if N % 2 == 0:
        for i in range(1, N, 2):
            d[i] = 0
    else:
        for i in range(0, N, 2):
            d[i] = 0
    
    
    for a in A:
        if a not in d: return 0
        else: d[a] += 1
    

    if N % 2 == 0:
        if all(d[a] == 2 for a in d):
            return pow(2, len(d.keys())) % div
        else:
            return 0
    else:
        if d[0] != 1: return 0
        else:
            del d[0]
            if all(d[a] == 2 for a in d):
                return pow(2, len(d.keys())) % div
            else:
                return 0

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

Solution (Python):
from collections import Counter
n=int(input())
a=list(map(int,input().split()))
c=Counter(a)

mod=10**9+7

def isExist():
    if n%2==0:
        for i in range(1, n, 2):
            if c[i]==2:
                continue
            else:
                return False
    elif n%2==1:
        for i in range(0, n, 2):
            if i==0 and c[i]==1:
                continue
            elif c[i]==2:
                continue
            else:
                return False
    return True

if isExist():
    ans=1
    for _ in range(int(n*0.5)):
        ans*=2
        ans%=mod
    print(ans)
else:
    print(0)

Solution (Python):

import sys
sys.setrecursionlimit(12345678)
import itertools
from collections import Counter
from collections import defaultdict
from collections import deque
import bisect
from heapq import heappush, heappop


def main():
    n = int(input())
    al = list(map(int, input().split()))
    al.sort()

    if len(al) % 2 == 1:  
        if al[0] != 0:
            print(0)
            return
        al = al[1:]

    for i in range(0, len(al), 2):
        if al[i] != al[i+1]:
            print(0)
            return

    mod = 10**9 + 7
    print(2 ** (len(al) // 2) % mod)


if __name__ == '__main__':
    main()

Solution (Python):
import math, string, itertools, fractions, heapq, collections, re,  array, bisect, sys, random, time, copy, functools
sys.setrecursionlimit(10**7)
inf = 10 ** 20
eps = 1.0 / 10**10
mod = 10**9+7
dd = [(-1, 0), (0, 1), (1, 0), (0, -1)]
ddn = [(-1, 0), (-1, 1), (0, 1), (1, 1), (1, 0), (1, -1), (0, -1), (-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 _pf(s): return print(s, flush=True)

N = _I()
A = LI()

"""
5
2 4 4 0 2

2なら、
xOxxx
xxxOx
の2通りしかない
N=9なら
xxxOxxxxx
xxxxxOxxx
の2通りしかない
4なら
Oxxxxと
xxxxO
しかない
これらをもとに確かめていく


Nが奇数の時
3
2 0 2
とすると成り立つ
4のとき
3 1 1 3
まずこれでできない場合をはじける

計算するまでもないのか。

2 4 4 0 2なら
前か後ろか、前か後ろかをかけるだけなので4

"""
if N == 1:
    if A[0] == 0:
        print(1)
    else:
        print(0)
    exit()

A.sort()

if N % 2 == 0:
    correct = list(range(1, N+1, 2))
    correct = correct + correct
    correct.sort()
else:
    
    correct = list(range(0, N+1, 2))
    correct = correct + correct
    correct.sort()
    correct = correct[1:]
if correct == A:
    ans = 2**(N//2)
    print(ans%mod)
else:
    print(0)

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

n=int(input())
s=list(map(int,input().split()))
s.sort()
t=n//2
ans=0
if n%2==0:
  check=[2*i+1 for i in range(t)]
  check*=2
  check.sort()
  

else:
  check=[2*i for i in range(t+1)]
  check*=2
  check.sort()
  check.remove(0)
  

if check==s:
  ans=(2**t)%a
print(ans)

Solution (Python):
import collections

N = int(input())
A = list(map(int,input().split(' ')))
C = collections.Counter(A)
L = C.most_common()

if N % 2 == 0:
  for i, j in L:
    if j == 2:
      pass
    else:
      print(0)
      exit()
else:
   for i, j in L:
    if j == 2:
      pass
    else:
      if i == 0:
        pass
      else:
        print(0)
        exit()
print(int((2**(N//2) % (10**9+7))))

Solution (Python):

import sys
import copy
import collections
from bisect import bisect_left
from bisect import bisect_right
from collections import defaultdict
from heapq import heappop, heappush, heapify
import math
import itertools
import random
 




 
INF = float('inf')
def inputInt(): return int(input())
def inputMap(): return map(int, input().split())
def inputList(): return list(map(int, input().split()))
 
def main():
    N = inputInt()
    A = inputList()
    base = []
    base_flg = []
    tmp = N // 2
    
    if N % 2 == 1:
        for i in range(0,N,2):
            base.append(i)
            base_flg.append(False)
    else:
        for i in range(1,N,2):
            base.append(i)
            base_flg.append(False)
            
    dic = {}
    for i in A:
        if i in dic:
            dic[i] += 1
        else:
            dic[i] = 1
            
    for k, v in dic.items():
        if k in base:
            if v == 2 and k != 0:
                ind = base.index(k)
                if base_flg[ind] == False:
                    base_flg[ind] = True
                else:
                    print(0)
                    sys.exit()
            else:
                if k == 0 and v == 1:
                    ind = base.index(k)
                    if base_flg[ind] == False:
                        base_flg[ind] = True
                    else:
                        print(0)
                        sys.exit()
                else:
                    print(0)
                    sys.exit()
        else:
            print(0)
            sys.exit()
            
    for i in base_flg:
        if i == False:
            print(0)
            sys.exit()
            
    tmp = N // 2    
    print((2**tmp) % 1000000007)
    
if __name__ == "__main__":
	main()

Solution (Python):
from collections import Counter

MOD = 10 ** 9 + 7

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

C = Counter(A)

b = 1 if N % 2 == 0 else 0

for key, value in C.items():
    if b == 0 and key == b and value != 1:
        print(0)
        exit()

    if key != b and value != 2:
        print(0)
        exit()
    b += 2

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

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

if n%2==0:
  for i in range(0,n//2+1,2):
    if not a[i]==a[i+1]==i+1:
      print("0")
      exit(0)
  print(2**(n//2)%(10**9+7))

else:
  b=[0]+a
  for i in range(0,(n+1)//2+1,2):
    if not b[i]==b[i+1]==i:
      print("0")
      exit(0)
  print(2**((n-1)//2)%(10**9+7))

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

if n%2==0:
  if 0 in a or len(set(a))!=n//2:flag=False
else:
  if len([0 for x in a if x==0])!=1 or len(set(a))!=n//2+1:flag=False

print(2**(n//2)%(10**9+7) if flag else "0")

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

n = N // 2
c = N - 1
for _ in range(n):
  a, b = A.pop(), A.pop()
  if (a != c) or (b != c):
    print(0)
    exit()
  c -= 2
      
if N % 2 == 1 and A[0] != 0:
    print(0)
    exit()
  
print(pow(2, n, (10**9 + 7)))

Solution (Python):
N = int(input())
A = sorted(list(map(int, input().split())))
cr_A = []
if N%2:
	cr_A.append(0)
	for i in range(1, N//2 + 1):
		cr_A.extend([2*i]*2)
else:
	for i in range(1, N//2 + 1):
		cr_A.extend([2*i - 1]*2)

if A == cr_A:
	if N > 1:
		print((2**(N//2))%(10**9 + 7))
	else:
		print(1)
else:
	print(0)

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

Solution (Python):
n=int(input())
ai=[int(x) for x in input().split()]

if (ai.count(0)==0 or ai.count(0)==1) and len(set(ai))==-(-n//2):
    ans=1
    for i in range(n//2):
        ans*=2
        ans%=10**9+7
    print(ans)
else:
    print(0)

Solution (Python):
N = int(input())
As = list(map(int, input().split()))
Ns = [0]*N
for A in As:
  Ns[A] += 1

r = 1
if N%2 == 1:
  if Ns[0] > 1:
    r = 0
  for i in range(1, N):
    if i%2 == 1 and Ns[i] > 0:
      r = 0
    if i%2 == 0 and Ns[i] > 2:
      r = 0
    if i%2 == 0 and (Ns[i] == 1 or Ns[i] == 2):
      r = (r*2)%1000000007
if N%2 == 0:
  for i in range(0, N):
    if i%2 == 0 and Ns[i] > 0:
      r = 0
    if i%2 == 1 and Ns[i] > 2:
      r = 0
    if i%2 == 1 and (Ns[i] == 1 or Ns[i] == 2):
      r = (r*2)%1000000007
print(r)

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

A.sort()

if N % 2 == 0:
  check = []
  for i in range(1, N + 1, 2):
    check.append(i)
    check.append(i)
  if A != check:
    print(0)
    exit(0)
else:
  check = [0]
  for i in range(2, N + 1, 2):
    check.append(i)
    check.append(i)
  if A != check:
    print(0)
    exit()

ans = 1
for _ in range(N // 2):
  ans *= 2
  ans %= MOD
print(ans)

Solution (Python):
from collections import Counter

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

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

Solution (Python):
import collections

N = int(input())
lst = list(map(int, input().split()))
c = dict(collections.Counter(lst))
ans = 2 ** (N // 2)
if (N % 2 != 0):
  for i in range(0, N, 2):
    if (i not in c.keys()):
      ans = 0
      break
    else:
      if (i == 0):
        if (c[i] != 1):
          ans = 0
          break
      else:
        if (c[i] != 2):
          ans = 0
          break
else:
  for i in range(1, N, 2):
    if (i not in c.keys()):
      ans = 0
      break
    else:
      if (c[i] != 2):
        ans = 0
        break
      
print(ans % ((10 ** 9) + 7))

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

Solution (Python):
import collections


n = int(input())
A = input().split()
d = collections.defaultdict(int)
for a in A:
    d[a] += 1
if n == 1:
    print(1)
    exit()
if n % 2 != 0:
    if '0' not in d or d['0'] != 1:
        print(0)
        exit()
    for i in range(2, n, 2):
        if str(i) not in d or d[str(i)] != 2:
            print(0)
            exit()
else:
    if '0' in d:
        print(0)
        exit()
    for i in range(1, n, 2):
        if str(i) not in d or d[str(i)] != 2:
            print(0)
            exit()
print(2**(n//2) % (10**9+7))

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

Solution (Python):
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)

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

A.sort()

if N % 2 == 1:
    check = [0]
    for i in range(2, N + 1, 2):
        check.append(i)
        check.append(i)
    if A != check:
        print(0)
        exit(0)
else:
    check = []
    for i in range(1, N + 1, 2):
        check.append(i)
        check.append(i)
    if A != check:
        print(0)
        exit(0)

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

print(ans)

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

if N % 2 == 0:
    hasZero = False
    for a in A:
        if a % 2 == 0:
            print(0)
            exit(0)

if N % 2 == 1:
    hasZero = False
    for a in A:
        if a == 0:
            if hasZero:
                print(0)
                exit(0)
            hasZero = True
        elif a % 2 == 1:
            print(0)
            exit(0)
    if not hasZero:
        print(0)
        exit(0)

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

print(ans)

Solution (Python):
import collections
n = int(input())
a = list(map(int, input().split()))
a = collections.Counter(a).most_common()
cnt = 1
for k, v in a:
    if k == 0 and v == 1 and n % 2 != 0:
        cnt *= 1
    elif k == 0 and v == 2 and n % 2 == 0:
        cnt *= 1
    elif k != 0 and v == 2:
        cnt *= 2
    else:
        print(0)
        exit()
    cnt %= (10 ** 9 + 7)
print(cnt)

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
b = []
for i in range(n):
    if n > ((i+1)*2-1):
        b.append(n-((i+1)*2-1))
    else:
        b.append(((i+1)*2-1)-n)

a.sort()
b.sort()
if a==b:
    print((2**(n//2))%(10**9+7))
else:
    print(0)

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

Solution (Python):
num = int(input())
mem = list(map(int, input().split()))

dic = {}
mod = 10 ** 9 + 7
zeros = 0
flag = True
for i in range(num):
    temp = mem[i]
    if not temp == 0:
        dic.setdefault(str(temp), 0)
        dic[str(temp)] += 1
    else:
        zeros += 1
for key in dic:
    if not dic[key] == 2:
        flag = False
        break
        
if (zeros == 0 or zeros == 1) and flag:
    print(int((2 ** (len(mem) // 2) % mod)))
else:
    print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
C = [0] * N
for a in A:
    C[a] += 1
if N % 2 == 1:
    if C[0] != 1:
        print(0)
        exit()
    for i in range(2, N, 2):
        if C[i] != 2:
            print(0)
            exit()
    print(2 ** ((N - 1) // 2) % 1000000007)
else:
    for i in range(1, N, 2):
        if C[i] != 2:
            print(0)
            exit()
    print(2 ** (N // 2) % 1000000007)