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):
import sys
input = sys.stdin.readline

def I(): return int(input())
def MI(): return map(int, input().split())
def LI(): return list(map(int, input().split()))

def main():
    mod=10**9+7
    N=I()
    A=LI()
    ans=1
    A.sort()
    L=[]
    if N%2==1:
        L.append(0)
        for i in range(N//2):
            for _ in range(2):
                L.append(2*(i+1))
                
    else:
        for i in range(N//2):
            for _ in range(2):
                L.append(2*i+1)
                
    if L==A:
        ans=pow(2,N//2,mod)
    else:
        ans=0
        
    print(ans)
        

main()

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

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

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

Solution (Python):
def resolve():
    n = int(input())
    S = list(map(int, input().split()))
    if n % 2 == 0:
        sum_a = (1 + max(S)) * (n // 2)
    else:
        sum_a = (2 + max(S)) * (n // 2)
    if sum(S) == sum_a:
        ans = pow(2, n // 2, (10 ** 9 + 7))
    else:
        ans = 0

    print(ans)

if __name__ == '__main__':
    resolve()

Solution (Python):
mod = 10**9+7
N = int(input())
A = [int(i) for i in input().split()]
if N % 2 == 1:
    import collections
    c = collections.Counter(A)
    for i in range(N):
        if i % 2 == 1:
            continue
        if i == 0:
            if c[i] != 1:
                print(0)
                exit()
        else:
            if c[i] != 2:
                print(0)
                exit()
if N % 2 == 0:
    import collections
    c = collections.Counter(A)
    for i in range(1,N):
        if i % 2 == 0:
            continue
        if c[i] != 2:
            print(0)
            exit()
def pow_k(a,n,mod):
    if n == 0:
        return 1
    if n % 2 ==0:
        return pow_k(a*a % mod,n//2,mod)
    else:
        return a * pow_k(a,n-1,mod) % mod
if N % 2 == 1:
    N -=1
print(pow_k(2,N//2,mod))

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

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

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

Solution (Python):
mod = 10**9 + 7
n = int(input())
a = sorted(list(map(int,input().split())))
 
if n % 2 == 0:
  for i in range(n//2):
    if not a[2*i] == a[2*i+1] == 2*i+1:
      print(0)
      exit()
else:
  if a[0] != 0:
    print(0)
    exit()
  for i in range(n//2):
    if not a[2*i+1] == a[2*i+2] == 2*i+2:
      print(0)
      exit()
print(pow(2, n//2) % mod)

Solution (Python):
mod = 10**9 + 7
n = int(input())
a = sorted(list(map(int,input().split())))
 
if n % 2 == 0:
  for i in range(n//2):
    if not a[2*i] == a[2*i+1] == 2*i+1:
      print(0)
      exit()
else:
  if a[0] != 0:
    print(0)
    exit()
  for i in range(n//2):
    if not a[2*i+1] == a[2*i+2] == 2*i+2:
      print(0)
      exit()
print(pow(2, n//2) % mod)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
b=[0]*(10**5)
mod=10**9+7
for i in range(n):
    b[a[i]]+=1
if n%2==0 and a.count(0)!=0:
    print(0)
    exit()
f=1
for i in range(n-1,-1,-2):
    if i==0:
        if b[i]!=1:
            f=0
            break
    elif b[i]!=2:
        f=0
        break
if f: 
    print(2**(n//2)%mod)
else: 
    print(0)

Solution (Python):


n = int(input())
a = sorted(list(map(int,input().split())))
p = 10 ** 9 + 7
l_odd = sorted([2*i-1 for i in range(1,n//2+1)]*2)
l_even = [0]+sorted([2*i for i in range(1,n//2+1)]*2)


if (n % 2 != 0 and a == l_even) or (n % 2 == 0 and a == l_odd):
    print(2**(n//2)%p)
else:
    print(0)

Solution (Python):
import numpy as np

div = 10**9 + 7

def Mod_Pow(a,n,mod):
    res = 1
    while (n > 0):
        if (n & 1):
            res = (res * a )% mod
        a = (a * a)% mod
        n >>= 1
    
    return res

def CountFrequency(my_list): 
  
    
    freq = {} 
    count_0 = 0
    for item in my_list: 
        if (item in freq): 
            freq[item] += 1
        else:             
            if item ==0:
                count_0+=1
            else:
                freq[item] = 1
    if N%2==0:
        return freq
    else:
        return freq, count_0

N = int(input())

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

if N%2 == 0:
    if all([ i ==2 for i in CountFrequency(A).values()]):
        ans = Mod_Pow(2,int(N/2),div)
    else:
        ans =0
    
            
else:
    count_0 = CountFrequency(A)[1]
    
    count_1 = list(CountFrequency(A)[0].values())
    if all([ i ==2 for i in count_1]) & (count_0 ==1):
        ans = Mod_Pow(2,int(N/2),div)
    else:
        ans =0
    
    
            
print(ans)

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 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):
mod = 10**9+7
N = int(input())
A = [int(x) for x in input().split()]

def po2(x) :
    ans = 1
    for i in range(x) :
        ans = (ans*2)%mod
    return ans

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

A.sort()
B.sort()

if A != B :
    print(0)
else :
    print(po2(N//2))

Solution (Python):
def get_pow(x, n):
    if n == 0:
        return 1
    ans = get_pow(x * x % 1000000007, int(n / 2))
    if n % 2 == 1:
        ans *= x
        ans %= 1000000007
    return ans

n = int(input())
a = list(map(int, input().split()))
c = [2] * ((n + 1) // 2)
if n % 2 == 1:
    c[0] = 1
for i in a:
    c[i // 2] -= 1
if c == [0] * len(c):
    print(get_pow(2, n // 2))
else:
    print(0)

Solution (Python):

import sys

N = int(input().strip())
A_list = list(map(int, input().rstrip().split()))


A_list.sort()


if N%2 == 0:
    i=0
    for x in range(int(N/2)):
        if A_list[i] == A_list[i+1] == 2*x + 1:
            i += 2
            continue
        else:
            
            print("0")
            sys.exit()

elif N%2 == 1:
    i=0
    for x in range( int((N-1)/2) ):
        if i == 0 and A_list[i] == 0:
            i += 1
            continue
        elif A_list[i] == A_list[i+1] == 2*x:
            i += 2
            continue
        else:
            
            print("0")
            sys.exit()


order = 1
for i in range(N//2):
    order = order * 2 % (10**9 + 7)

print(order)

Solution (Python):
mod = 10 ** 9 + 7
n = int(input())
a_i = list(map(int, input().split()))
a_i.sort()
ans = 1
if max(a_i) >= n: ans = 0
else:
    for x in range(n //2):
        if n % 2 == 0:
            if a_i[2 * x] != 2 * x + 1 or a_i[2 * x + 1] != 2 * x + 1: ans = 0
            else: 
                ans *= 2
                ans = ans % mod
        elif a_i[0] == 0 and n % 2 != 0:
            if a_i[2 * (x + 1) - 1] != 2 * (x + 1) or a_i[2 * (x + 1)] != 2 * (x + 1): ans = 0
            else: 
                ans *= 2
                ans = ans % mod
        else: ans = 0
print(ans % mod)

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
A.sort()
if N % 2 == 0:
  for i in range(1,N,2):
    for n in range(2):
      if not A[i + n - 1] == i:
        print(0)
        exit()
  print(2**(N//2)%1000000007)
else:
  for i in range(0,N-1,2):
      for n in range(2):
        if i == 0 and n == 0:
          continue
        if not A[i + n - 1] == i:
          print(0)
          exit()
  print(2**((N-1)//2)%1000000007)

Solution (Python):
import sys
from io import StringIO
import unittest

def resolve():
    readline=sys.stdin.readline
    n=int(readline())
    ai=list(map(int, readline().split()))

    x=[0]*(10**5+1)
    for a in ai:
        x[a]+=1
    
    k=n-1
    x2=0
    while k>=0:
        if k==0 and x[k]==1:
            x2+=0
        elif x[k]==2:
            x2+=1
        else:
            print(0)
            return
        k-=2
    
    print(pow(2,x2,10**9+7))
resolve()

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):
n=int(input());print([0,2**(n//2)%(10**9+7)][sorted(map(int,input().split()))==[i+(i+n+1)%2for i in range(n)]])

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

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

Solution (Python):
n=int(input())
numlist=list(map(int,input().split()))
num=[]
for i in range(n):
  num.append(0)
count=0
for i in numlist:
  num[i]+=1
  if num[i]==3:
    count=-1
    break
  elif i==0 and num[0]==2:
    count=-1
    break
  else:
    pass
if count==-1:
  print(0)
else:
  count=2**(n//2)
  count=count%(10**9+7)
  print(count)

Solution (Python):

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

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

Solution (Python):







import sys
read = sys.stdin.readline


def read_ints():
    return list(map(int, read().split()))


def read_a_int():
    return int(read())


N = read_a_int()
A = read_ints()

from collections import Counter
A_cnt = Counter(A)


def end():
    print(0)
    exit()


if N & 1:
    if A_cnt[0] != 1:
        end()
    for i in range(2, N, 2):
        if A_cnt[i] != 2:
            end()
else:
    for i in range(1, N, 2):
        if A_cnt[i] != 2:
            end()

print(pow(2, N // 2, 10**9 + 7))

Solution (Python):







import sys
read = sys.stdin.readline


def read_ints():
    return list(map(int, read().split()))


def read_a_int():
    return int(read())


N = read_a_int()
A = read_ints()

from collections import Counter
A_cnt = Counter(A)


def end():
    print(0)
    exit()


if N & 1:
    if A_cnt[0] != 1:
        end()
    for i in range(2, N, 2):
        if A_cnt[i] != 2:
            end()
else:
    for i in range(1, N, 2):
        if A_cnt[i] != 2:
            end()

print(pow(2, N // 2, 10**9 + 7))

Solution (Python):
def main():
    people_num = int(input())
    information = sorted(list(map(int, input().split())))
    unique = len(set(information))
    answer = 0
    if unique * 2 == people_num + people_num % 2:
        if people_num > 1 and information[1] > 0:
            answer = 2 ** (unique - people_num % 2)
        elif people_num == 1 and information[0] == 0:
            answer = 1
    print(answer % (10 ** 9 + 7))


if __name__ == '__main__':
    main()

Solution (Python):


import collections
N = int(input())
A = list(map(int,input().split()))
A.sort()
mod = 10 ** 9 + 7
Flg = True
if N % 2 == 1:
    a = A.pop(0)
    if a != 0:
        Flg = False

k = (N % 2) + 1
for i in range(N //2):
    if A[i *2] != k or A[i * 2 + 1] != k:
        Flg = False
    k += 2
    
if Flg:
    ans = (2 ** (N // 2)) % mod
else:
    ans = 0
    
print(ans)

Solution (Python):

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

MOD=10**9+7
flg=True
k=1

if N%2==1:
    k=2
    a=A.pop(0)
    if a!=0:
        flg=False
        
for i in range(N//2):
    if A[i*2]!=k or A[i*2+1]!=k:
        flg=False
    k+=2
    
if flg:
    ans=1
    for i in range(N//2):
        ans*=2
        ans=ans%MOD
else:
    ans=0

print(ans)

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

if n % 2 == 0:
    for k,v in a.items():
        if v != 2:
            print(0)
            sys.exit()

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

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

for i in a:
    cnt[i] += 1

ans = 1
if n % 2 == 0:
    for _ in range(n // 2):
        ans *= 2
        ans %= mod
    if cnt[0] == 0:
        check = [2 * i + 1 for i in range(n // 2)]
        for i in check:
            if cnt[i] != 2:
                ans = 0
                break
    else:
        ans = 0

else:
    for _ in range((n-1)//2):
        ans *= 2
        ans %= mod
    if cnt[0] == 1:
        check = [2 * i + 2 for i in range((n-1)//2)]
        for i in check:
            if cnt[i] != 2:
                ans = 0
                break

    else:
        ans = 0

print(ans)

Solution (Python):
MOD=1000000007
def modpow(a,n,mod):
    res=1
    a=a%mod
    while(n>0):
        if(n&1):
            res=res*a%mod
        a=a*a%mod
        n>>=1
    return res

N=int(input())
A=list(map(int,input().split()))
cnt=[0]*100001
for i in range(N):
    cnt[A[i]]+=1
if(N%2==1):
    if(cnt[0]!=1):
        print(0)
        exit()
    for i in range(2,N,2):
        if(cnt[i]!=2):
            print(0)
            exit()
elif(N%2==0):
    for i in range(1,N,2):
        if(cnt[i]!=2):
            print(0)
            exit()
print(modpow(2,N//2,MOD))

Solution (Python):

def mod_(b, n, mod):
    res = 1
    while n > 0:
        if n & 1:
            res = res * b % mod
        b = b * b % mod
        n >>= 1
    return int(res)

def main():

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

    n = ((N+1) >> 1)
    li = [0]*n



    for a in A:
        li[a >> 1] += 1

    if N & 1:
        if li[0] != 1:
            print(0)
        elif li.count(2) != n-1:
            print(0)
        else:
            c = n-1
            print(2 ** c % (10**9+7))
    else:
        if li.count(2) != n:
            print(0)
        else:
            c = n
            print(2 ** c % (10**9+7))

main()

Solution (Python):
import numpy as np

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

if len(A)%2 == 0:
    result = (2**(len(A)//2))%(10**9+7)
    a = np.arange(1, len(A), 2).tolist()
    a = sorted(a+a)
    if a == A:
        pass
    else:
        result = 0
else:
    result = 2**(len(A)//2)%(10**9+7)
    a = np.arange(2, len(A), 2).tolist()
    a = sorted([0]+a+a)
    if a == A:
        pass
    else:
        result = 0
print(result)

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

f = 1

if n%2 == 0:
    ans = [2]*(n//2)
    
    for i in range(n):
        if a[i]%2 == 0:
            f = 0
            break
        x = a[i]//2
        ans[x] -= 1

else:
    ans = [2]*((n+1)//2)
    ans[0] -= 1
    for i in range(n):
        if a[i]%2 != 0:
            f = 0
            break
        x = a[i]//2
        ans[x] -= 1

for i in range(len(ans)):
    if ans[i] != 0:
        f = 0
        break

if f == 0:
    print(f)
else:
    print((2**(n//2))%1000000007)

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

    if n%2==1:
        if 0 not in a:
            print(0)
            exit()
        else:
            if a[0]!=1:
                print(0)
                exit()
            else:
                a[0]=2
    
    for k,v in a.items():
        if v!=2 or (n-k-1)%2==1:
            print(0)
            exit()
            
    print(2**(n//2)%mod)  
if __name__=='__main__':
    main()

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

    numlist = dict()

    if n % 2 == 1:
        for i in range(0, n+1, 2):
            numlist[i] = []
    else:
        for i in range(1, n+1, 2):
            numlist[i] = []

    for aa in a:
        if aa not in numlist.keys():
            print('0')
            exit()
        numlist[aa].append(aa)

    for num in numlist:
        if num == 0 and len(numlist[num]) != 1:
            print('0')
            exit()
        elif num == 0 and len(numlist[num]) == 1:
            continue
        elif len(numlist[num]) != 2:
            print('0')
            exit()

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

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

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

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

if n%2 == 1:
    m = (n+1)//2
    l =[0]*m
    for i in range(n):
        if (n-A[i]-1)%2 != 0:
            print(0)
            exit()
        else:
            id = (n-A[i]-1)//2
            l[id] += 1
    
    ans = 1
    for i in range(m):
        
        if i != m -1:
            if l[i] != 2:
                print(0)
                exit()
            else:
                ans *= l[i]
                ans %= mod
        else:
            if l[i] != 1:
                print(0)
                exit()
            else:
                ans *= l[i]
                ans %= mod
    print(ans)

else:
    m = n//2
    l =[0]*m
    for i in range(n):
        if (n-A[i]-1)%2 != 0:
            print(0)
            exit()
        else:
            id = (n-A[i]-1)//2
            l[id] += 1
    
    ans = 1
    for i in range(m):
        
        if l[i] != 2:
            print(0)
            exit()
        else:
            ans *= l[i]
            ans %= mod
    print(ans)

Solution (Python):
import math
import sys

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

li = [0] * N
count = 0

if N % 2 == 0:
  t = 1
else:
  t = 0

for a in A:
  if a == 0:
    li[math.floor((N-1)/2)] += 1
    count += 1
    
    if count == 2:
      print(0)
      sys.exit()

    continue

  li[math.floor((N-1)/2)-math.floor(a/2)] += 1
  li[math.floor((N-1)/2)+math.floor(a/2)+t] += 1

ans = 1

for i in range(0, math.floor(N/2)):
  ans *= li[i]

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

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

from collections import Counter
C = Counter(A)
if len(A)%2 == 0:
  for k, v in C.items():
    if v != 2:
      print(0)
      exit()
else:
  for k, v in C.items():
    if k == 0:
      if v != 1:
        print(0)
        exit()
    else:
      if v!=2:
        print(0)
        exit()

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

Solution (Python):
from collections import defaultdict
count=defaultdict(lambda:0)
N=int(input())
A=list(input().split(" "))
k=-1
for i in range(N):
    count[A[i]]+=1
if N%2==1:
    if count["0"]!=1:
        k=0
    for i in range(1,N//2+1):
        if count[str(2*i)]!=2:
            k=0
else:
    for i in range(1,N//2+1):
        if count[str(2*i-1)]!=2:
            k=0
if k!=0:
    if N%2==0:
        print(2**(len(count.keys()))%(10**9+7))
    else:
        print(2**(len(count.keys())-1)%(10**9+7))
else:
    print(0)

Solution (Python):
n = int(input())
A = list(map(int, input().split()))
r = n%2

d = [0]*n
for a in A:
    if a%2 == r:
        print(0)
        break
    d[a] += 1
    if (d[a] > 2) or (a == 0 and d[0] > 1):
        print(0)
        break
else:
    print(2**(n//2) % (10**9+7))

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

MOD=10**9+7

if N%2:
    arr=sorted([0]+list(range(2,N))[::2]*2)
else:
    arr=sorted(list(range(1,N))[::2]*2)

print(2**(N//2)%MOD if A == arr else 0)

Solution (Python):
from itertools import groupby


def main():
    n = int(input())
    xs = sorted(list(map(int, input().split())))

    if n == 1:
        if xs[0] == 0:
            print(1)
        else:
            print(0)
        return

    xxs = [list(it) for k, it in groupby(xs)]

    if len([xs for xs in xxs if len(xs) != 2 and xs[0] != 0]) > 0:
        print(0)
        return

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


main()

Solution (Python):
import collections
n = int(input())
dat = list(map(int, input().split()))
dat.sort()
f = True
if n % 2 == 0: 
    for i in range(n):
        if dat[i] != 2 * (i // 2) + 1:
            f = False
    if f:
        print(2 ** (n // 2) % (1000000000+7) )
else: 
    if dat[0] != 0:
        f = False
    for i in range(n - 1):
        if dat[i + 1] != 2 * (i//2 + 1):
            f = False
    if f:
        print(2** (n //2 ) % (1000000000+7) )
if f is False:
    print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
judge = 1
while 0 in A:
    A.remove(0)

A_ = list(set(A))
A_.sort()
for i in range(len(A_) - 1):
    if A_[i+1] == A_[i]+2:
        judge = 1
    else:
        judge = 0

if len(set(A)) == len(A)/2 and judge:
    print((2 ** (len(A) // 2)) % (10**9 +7))
else:
    print(0)

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
a.sort()
if n%2 == 0:
    a_l = a[0::2]
    a_r = a[1::2]
    flag = True
    key = 1
    for i,j in zip(a_l,a_r):
        if i!=key or j!=key:
            flag = False
            break
        key += 2
    if flag:
        print(2**(n//2)%(10**9+7))
    else:
        print(0)
else:
    a_l = a[1::2]   
    a_r = a[2::2]
    flag = True
    key = 2
    for i,j in zip(a_l,a_r):
        if i!=key or j!=key:
            flag = False
            break
        key += 2
    if flag:
        print(2**(n//2)%(10**9+7))
    else:
        print(0)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
B=[]
if N%2 ==0:
    for a in range(1, N, 2):
        B.append(a)
    B+=B
    if sorted(A) == sorted(B):
        print(2**len(set(A))%(10**9+7))
    else:
        print(0)
else:
    for a in range(2, N, 2):
        B.append(a)
    B=B+B+[0]
    if sorted(A) == sorted(B):
        print(2**(len(set(A))-1)%(10**9+7))
    else:
        print(0)

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

if N%2==0:
    for i in range(1,N,2):
        x[i]=0
    for i in range(N):
        if A[i] in x:
            x[A[i]]+=1
        else:
            y[A[i]]=1
    for idx in x:
        if idx==0:
            if x[idx]<1:
                flag=False
            continue
        if x[idx]!=2:
            flag=False
    ans=1
    if flag:
        for idx in x:
            ans=ans*x[idx]
    else:
        print(0)
        exit()
    ans=ans%MOD
    print(ans)

else:
    for i in range(0,N,2):
        x[i]=0
    for i in range(N):
        if A[i] in x:
            x[A[i]]+=1
        else:
            y[A[i]]=1
    for idx in x:
        if idx ==0:
            if x[idx]<1:
                flag=False
            continue
        if x[idx]!=2:
            flag=False
    ans=1
    if flag:
        for idx in x:
            ans=ans*x[idx]
    else:
        print(0)
        exit()
    ans=ans%MOD
    print(ans)

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

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

if len(set(a))==(n+1)//2:
    a = sorted(a)
    if n % 2:
        del a[0]
        check(int((n-1)/2), a)
    else:
        check(int(n/2), a)
else:
    print(0)

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

a.sort(reverse = True)

if n % 2 == 1:
  del(a[-1])
r = 1
turn = 0
start = n - 1
check = True

for i in range(0, len(a)):
  turn += 1  
  if a[i] != start:
    r = 0
  if turn > 1:    
    turn = 0
    start -= 2

if not r:
  print(0)
else:
  
  r = 2**(n//2) % (10**9 + 7)
  print(r)

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

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
A.sort()
if N%2==1:
    collect=list(range(0,N))[::2]*2
    collect.remove(0)
elif N % 2 == 0:
    collect = list(range(1, N))[::2] * 2

collect.sort()
if collect!=A:
    print(0)
else:
    print(2**(N//2)%(10**9+7))

Solution (Python):
N = int(input())
A = sorted(list(map(int, input().split())), reverse=True)
n = N-1
for i in range(N//2):
  if A[2*i]!=n or A[2*i+1]!=n:
    print(0)
    exit()
  n -= 2
  
if N&1 and A[-1]!=0:
  print(0)
  exit()

print((1<<N//2)%(10**9+7))

Solution (Python):
import collections

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

b = collections.Counter(a)
c = b.most_common()
c.sort(key=lambda x: x[0])
cnt = 1
if n % 2 == 1:
    cnt = 0

for i, j in c:
    
    if cnt == 0:
        if j != 1:
            print(0)
            exit()
        else:
            cnt += 2
    else:
        if i != cnt or j != 2:
            print(0)
            exit()
        else:
            cnt += 2

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

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
a.sort()
if n % 2 == 1:
    if a[0] != 0:
        print(0)
    else:
        for i in range(2, n, 2):
            if not i == a[i-1] == a[i]:
                print(0)
                break
        else: print((2**(n//2))%1000000007)
else:
    for i in range(1, n, 2):
        if not i == a[i-1] == a[i]:
            print(0)
            break
    else: print((2**(n//2))%1000000007)

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

Solution (Python):
import collections
n=int(input())
l=list(input().split())
c=collections.Counter(l)
if n%2==0:
  f=all(x==2 for x in c.values())
else:
  g=c.pop("0")==1
  f=all(x==2 for x in c.values()) and g
print(2**(n//2)%1000000007 if f==True else 0)

Solution (Python):
MOD=10**9+7
class Fp(int):
    def __new__(self,x=0):return super().__new__(self,x%MOD)
    def inv(self):return self.__class__(super().__pow__(MOD-2,MOD))
    def __add__(self,value):return self.__class__(super().__add__(value))
    def __sub__(self,value):return self.__class__(super().__sub__(value))
    def __mul__(self,value):return self.__class__(super().__mul__(value))
    def __floordiv__(self,value):return self.__class__(self*self.__class__(value).inv())
    def __pow__(self,value):return self.__class__(super().__pow__(value%(MOD-1), MOD))
    __radd__=__add__
    __rmul__=__mul__
    def __rsub__(self,value):return self.__class__(-super().__sub__(value))
    def __rfloordiv__(self,value):return self.__class__(self.inv()*value)
    def __iadd__(self,value):self=self+value;return self
    def __isub__(self,value):self=self-value;return self
    def __imul__(self,value):self=self*value;return self
    def __ifloordiv__(self,value):self=self//value;return self
    def __ipow__(self,value):self=self**value;return self
    def __neg__(self):return self.__class__(super().__neg__())


N = int(input())
A = sorted(map(int, input().split()))
ans = Fp(1)
if N & 1:
    if all(a == (i + 1) // 2 * 2 for i, a in enumerate(A)):
        for i in range(N//2):
            ans *= 2
    else:
        ans = 0
else:
    if all(a == i // 2 * 2 + 1 for i, a in enumerate(A)):
        for i in range(N//2):
            ans *= 2
    else:
        ans = 0
print(ans)

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

if N % 2 == 1:
  cnt = set()
  for (key, value) in Counter(A).items():
    if key == 0:
      if value != 1:
        print(0)
        exit()

    else:

      if key % 2 != 0 or value != 2:
        print(0)
        exit()

      cnt.add(key)

else:
  cnt = set()
  for (key, value) in Counter(A).items():
    if key % 2 != 1 or value != 2:
      print(0)
      exit()

    cnt.add(key)

if len(cnt) != N // 2:
  print(0)
  exit()

print(2 ** len(cnt) % mod)

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)