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 math
import sys
import collections

n = int(input())
a = list(map(int, input().split()))
ans = 0
counts = collections.Counter(a)
mod = 10**9+7


if n % 2 == 1:
    
    if counts[0] != 1:
        print(0)
        sys.exit()
    for i in range(2, n-1, 2):
        if counts[i] != 2:
            print(0)
            sys.exit()
else:
    for i in range(1, n-1, 2):
        if counts[i] != 2:
            print(0)
            sys.exit()

ans = 2**(n//2)

print(ans%mod)

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

Solution (Python):
from collections import Counter

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

c=Counter(aa)

ans = 0
z_flag = False

if n%2 == 1:  
  if c[0] != 1:  
    z_flag = True    
else:
  if c[0] != 0:  
    z_flag = True    
    
ans = 1      
for k,v in c.items():
  if k==0:
    pass
  else:
    if v//2 != 1:
      z_flag = True
      break
    else:
      ans *= v      

if z_flag:
  ans = 0
  
print(ans % (10**9+7))

Solution (Python):
n=int(input())
import numpy as np
a=np.sort(np.array(input().split(),dtype=int))
DIV=10**9+7
if n%2==1:
  if a[0]!=0:
    print(0)
    exit(0)
  a=a[1:]
  a-=1    
for i in range(len(a)):
  if a[i]!=i+(i%2==0):
    print(0)
    exit(0)
print((2**(len(a)//2))%DIV)

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

DIV=10**9+7

if n%2==1:
  if a[0]!=0:
    print(0)
    exit(0)
  a=a[1:]
  for i in range(len(a)):
    a[i]=a[i]-1
    
for i in range(len(a)):
  if a[i]!=i+(i%2==0):
    print(0)
    exit(0)
    
print((2**(len(a)//2))%DIV)

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

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

sd = sorted(d.items(), key=lambda x: x[0])

if N % 2 == 0:
    if sd[0][1] == 1:
        print(0)
        exit()
else:
    if sd[0][1] != 1:
        print(0)
        exit()
ans = 1
for i in range(N // 2):
    ans *= 2
    ans %= INF

print(ans)

Solution (Python):
from collections import Counter
import math
N = int(input())
A = list(map(int,input().split()))
A_count = Counter(A)
count_item = list(A_count.items())
count_item.sort()
start = 1 - (N % 2)
for i in range(math.ceil(N / 2)):
    if i == 0 and N % 2 == 1:
        if count_item[i][0] == 0 and count_item[i][1] != 1:
            print("0")
            exit()
    else:
        if count_item[i][0] != i * 2 + (1 - (N % 2)) or count_item[i][1] != 2:
            print("0")
            exit()
print(2 ** (N // 2) % (10 ** 9 + 7))

Solution (Python):
import sys
from collections import Counter
n = int(input())
MOD = 10**9 + 7
a_ls = [int(i) for i in sys.stdin.readline().split()]
ct = Counter(a_ls)
_sum = 0
res = 1
flg = (n + 1) % 2
if flg == 0:
    res = 0 if ct.get(0) != 1 else 1
for i in range(1, max(a_ls) + 1):
    if flg == i % 2:
        if ct.get(i) == 2:
            res = res * 2 % MOD
        else:
            res = 0
            break
    else:
        if ct.get(i) is None:
            continue
        else:
            res = 0
            break
    if res == 0:
        break
print(res)

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

for i in range(N):
  if A[i] != i + (i % 2 == N % 2):
    print(0)
    exit()

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

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
 
memo = {}
ans = 0
 
for a in A:
  v = str(a)
  if v in memo:
    memo[v] += 1
  else:
    memo[v] = 1

result = False
for key in memo.keys():
  if key == '0':
    if N%2 == 0:
      result=True
      break
    if memo[key] != 1:
      result=True
      break
  elif memo[key] != 2:
    result=True
    break
    
if not result:
  x = len(memo.keys())
  if N%2 != 0:
    x-=1
  ans = 2**x
  
div = 10**9 + 7
print(ans%div)

Solution (Python):
import sys
from functools import reduce
import copy
import math
from pprint import pprint
import collections
import bisect
import itertools


sys.setrecursionlimit(4100000)


def inputs(num_of_input):
    ins = [input() for i in range(num_of_input)]
    return ins


def int_inputs(num_of_input):
    ins = [int(input()) for i in range(num_of_input)]
    return ins


def solve(inputs):
    A = string_to_int(inputs[0])
    A.sort()
    apper = collections.Counter()

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

    start = 1 if len(A) % 2 == 0 else 0
    for i in range(start, len(A), 2):
        if i not in apper:
            return 0
        if i == 0 and apper[0] != 1:
            return 0
        if i != 0 and apper[i] != 2:
            return 0
    if 0 in apper:
        apper.pop(0)

    return (2 ** len(apper)) % 1000000007


def string_to_int(string):
    return list(map(lambda x: int(x), string.split()))


if __name__ == "__main__":
    input()
    ret = solve(inputs(1))
    print(ret)

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

Solution (Python):
from collections import defaultdict

def possible():
    if N%2==0:
        for cnt in cnt_dict.values():
            if cnt != 2:
                return False
        return True
    else:
        for i, cnt in enumerate(cnt_dict.values()):
            if i==0:
                if cnt != 1:
                    return False
            else:
                if cnt != 2:
                    return False
        return True

N = int(input())
A = list(map(int, input().split()))
num = N//2

cnt_dict = defaultdict(list)

if N%2==0:
    for i in range(1, N, 2):
        cnt_dict[i] = 0
else:
    for i in range(0, N, 2):
        cnt_dict[i] = 0
for a in A:
    if not(a in cnt_dict.keys()):
        flag=False
    else:
        cnt_dict[a]+=1
        flag=True

if __name__ == "__main__":    

    if possible() and flag:
        mod = 10**9+7
        res = 1
        for i in range(1, num+1):
            res = res*2%mod
        print(res)
    else:
        print(0)

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] % 2 == 0:
            print(0)
            exit()
        elif a[i] != a[i+1]:
            print(0)
            exit()

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

num = n // 2
ans = (2 ** num) % 1000000007
print(ans)

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

    C = [0] * N
    for ai in A:
        C[ai] += 1
    
    flag = True
    if N % 2 == 1:
        for i, n in enumerate(C):
            if i == 0:
                if n != 1:
                    flag = False
            elif i % 2 == 0:
                if n != 2:
                    flag = False
            else:  
                if n != 0:
                    flag = False
        if not flag:
            ans = 0
        else:
            ans = 2 ** ((N - 1)//2)
    else:
        for i, n in enumerate(C):
            if i % 2 == 1:
                if n != 2:
                    flag = False
            else:
                if n != 0:
                    flag = False
        if not flag:
            ans = 0
        else:
            ans = 2 ** (N // 2)

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




if __name__ == "__main__":
    main()

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
mod=10**9+7
ans=pow(2,N//2,mod)
judge=[0]*N
if N%2==0:
  for a in A:
    if (a>=N)or(a%2==0)or(judge[a]>=2):
      ans=0
      break
    judge[a]+=1
    
else:
  if A.count(0)!=1:
    ans=0
    
  else:
    for a in A:
      if (a>=N)or(a%2==1)or(judge[a]>=2):
        ans=0
        break
      judge[a]+=1
      
print(ans)

Solution (Python):
from sys import stdin
import math
from itertools import groupby

n = int(stdin.readline().rstrip())
li = list(map(int,stdin.readline().rstrip().split()))

li.sort()

if len(li) == 1:
    if li[0] != 0:
        print(0)
        exit()
    else:
        print(1)
        exit()

if li[0] == 0 and li[1] == 0:
    print(0)
    exit()
    
lin = []
for key, value in groupby(li):
    lin.append(len(list(value)))

point = 1

for i in lin:
    if i >= 3:
        print(0)
        exit()
    point *= math.factorial(i)
    point %= 10**9+7

print(point)

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

flag = False
ans = 0
b = [0] * n


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

if b == sorted(a):
    ans = (2 ** (n // 2)) % (10 ** 9 + 7)

print(ans)

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

else:
	for i in range(n//2):
		if a[i*2]!=i*2+1 or a[i*2+1]!=i*2+1:
			judge=False
			break
	if judge:
		ans=2**(n//2)
	else:
		ans=0
		
print(ans%1000000007)

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

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

Solution (Python):

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

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

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

Solution (Python):
from collections import Counter

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

res = 2 ** (n // 2)
res %= 10**9 + 7

if n % 2 == 1:
    if 0 not in a:
        res = 0
    elif a[0] != 1:
        res = 0
    for i in range(2, n, 2):
        if a[i] != 2:
            res = 0
else:
    for i in range(1, n, 2):
        if a[i] != 2:
            res = 0

print(res)

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


def kaijo(n):
  temp=1
  for i in range(n):
    temp*=2
    temp%=mod
  return temp


if n%2:
  ki=[0]*((n+1)//2)
  for i in a:
    if i==0: 
      ki[0]+=2
    elif i%2==0: 
      ki[i//2]+=1
  if len(set(ki))==1:
    print(kaijo((n-1)//2))
  else:
    print(0)
else:
  ki=[0]*(n//2)
  for i in a:
    if i%2: 
      ki[i//2]+=1
  if len(set(ki))==1:
    print(kaijo((n//2)))
  else:
    print(0)

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








def check(L):
    if len(L) % 2 == 1:
        C = [x for x in range(2,len(L), 2)]*2 + [0]
        C = sorted(C)
        if L == C:
            return True
        else:
            return False
    elif len(L) % 2 == 0:
        C = [x for x in range(1,len(L), 2)]*2
        C = sorted(C)
        if L == C:
            return True
        else:
            return False

if check(A) == True:
    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_sorted = sorted(a)
b_sorted = sorted([abs(i) for i in range(-(n - 1), n, 2)])

if a_sorted == b_sorted :
    if n % 2 == 1:
        print((2 ** ((n - 1) // 2)) % (10 ** 9 + 7))
    elif n % 2 == 0 :
        print((2 ** (n // 2)) % (10 ** 9 + 7))
else :
    print(0)

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

Solution (Python):
def solve():
    N = int(input())
    Ai = tuple(map(int, input().split()))
    P = 10**9 + 7

    
    

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

    if not (len(Ai) == len(lis) and sorted(Ai) == sorted(lis)):
        return 0

    if N % 2 == 0:
        return pow(2, len(lis) // 2, P)
    else:
        return pow(2, (len(lis) - 1) // 2, P)


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

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
a.sort()
mod = 10**9+7
flag = 0
flag_2 = 0
if n % 2 == 0:
  flag = -1
  for i in range(0,n,2):
    flag += 2
    if a[i] != flag or a[i+1] != flag:
      flag_2 = 1
  if flag_2 == 0:
    print(2**(n//2) % mod)
  else:
    print(0)
else:
  if a[0] != 0:
    flag_2 = 1
  for i in range(1,n,2):
    flag += 2
    if a[i] != flag or a[i+1] != flag:
      flag_2 = 1
  if flag_2 == 0:
    print(2**(n//2) % mod)
  else:
    print(0)

Solution (Python):

import math
mod = 10**9+7
N = int(input())
A = list(map(int,input().split()))
A.sort()
if N%2 == 0:
    n = N//2
    flag = 0
    for i in range(N):
        I = i//2 * 2 + 1
        if A[i] != I:
            flag = 1
            break
    if flag == 1:
        print(0)
    else:
        print(2**n%mod)
    
else:
    n = N//2
    flag = 0
    for i in range(N):
        if i == 0:
            if A[0] != 0:
                flag = 1
                break
        else:
            I = (i+1)//2 * 2
            if A[i] != I:
                flag = 1
                break
    if flag == 1:
        print(0)
    else:
        print(2**n%mod)

Solution (Python):
import collections
n=int(input())
a=[int(i) for i in input().split()]
def is_even(n):
    if(n%2==0):
        even=True
    else:
        even=False
    return even

c = collections.Counter(a)
ans=1
if(is_even(n)==True):
    for num,count in c.items():
        if(is_even(num)==True):
            print(0)
            exit()
        if(count>=3):
            print(0)
            exit()
        ans*=2
else:
    for num,count in c.items():
        if(is_even(num)==False):
            print(0)
            exit()
        if(count>=3):
            print(0)
            exit()
        if(count>=2 and num==0):
            print(0)
            exit()
        if(num!=0):
            ans*=2
print(ans%(10**9+7))

Solution (Python):

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

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

def two_n (n):
    mod = 10**9 + 7
    ret = 1
    for _ in range(n):
        ret *= 2
        ret %= mod
    return ret

bl = [0 for _ in range(n)]
for aa in a:
    bl[aa] += 1

report = True

if n % 2 == 0:
    for i in range(n):
        if i % 2 == 1 and bl[i] != 2:
            report = False
            break
        elif i % 2 == 0 and bl[i] != 0:
            report = False
            break
    
elif n % 2 == 1:
    for i in range(n):
        if i % 2 == 1 and bl[i] != 0:
            report = False
            break
        elif i % 2 == 0 and i > 0 and bl[i] != 2:
            report = False
            break
        elif i == 0 and bl[i] != 1:
            report = False

if report:
    print(two_n(n//2))
else:
    print(0)

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

Solution (Python):
mod = 10**9 + 7
from collections import Counter

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

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

print(ans)

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

Solution (Python):


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


b = [abs(i) for i in range(-n+1, n, 2)]
b.sort()
if a==b:
    result = 2**(n//2)%(10**9+7)
else:
    result = 0
print(result)

Solution (Python):
import collections

N = int(input())
A = list(map(int, input().split()))
counter = collections.Counter(A)
flag = True

if N % 2 != 0:
    for i in range(0, max(A) + 1):
        if i == 0:
            if counter[i] != 1:
                flag = False
                break
        elif (i % 2 == 0 and counter[i] != 2) or (i % 2 != 0 and counter[i] != 0):
            flag = False
            break                
    ans = 2 ** (max(A) // 2) % (10**9 + 7)

else:
    for i in range(0, max(A) + 1):
        if (i % 2 == 0 and counter[i] != 0) or (i % 2 != 0 and counter[i] != 2):
            flag = False
            break
    ans = 2 ** (max(A) // 2 + 1) % (10**9 + 7)

if flag:
    print(ans)
else:
    print(0)

Solution (Python):
N = int(input())
d = {}
if N % 2 == 0:
    for i in range(N//2):
        d[2*i+1] = 0
else:
    for i in range(N//2+1):
        d[2*i] = 0
A = list(map(int,input().split()))
x = 1
for i in range(N):
    if A[i] in d:
        if d[A[i]] >= 2:
            x = 0
            break
        else:
            d[A[i]] += 1
    else:
        x = 0
        break
y = 1
if N % 2 == 1:
    if d[0] != 1:
        y = 0
e = 10**9 + 7
ans = (2**(N//2))*x*y%e
print(ans)

Solution (Python):
n=int(input())
A=sorted((map(int,input().split())))
G=sorted([2*(i+1) for i in range(n//2)]*2+[0])
K=sorted([(2*i+1) for i in range(n//2)]*2)
if n%2:
	if A!=G:
		print(0)
		exit()
else:
	if A!=K:
		print(0)
		exit()
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.count(0)!=1:
    print(0)
    exit()
  else:
    for i in range(1,n,2):
      if a[i]!=a[i+1] or a[i]!=i+1:
        print(0)
        exit()
else:
  for i in range(0,n,2):
    if a[i]!=a[i+1] or a[i]!=1+i:
      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
a.sort()
if n%2==0:
    for i in range(n):
        if a[i]==(i//2)*2+1:
            continue
        else:
            print(0)
            break
    else:
        print(pow(2,n//2,mod))
else:
    for i in range(n):
        if a[i]==((i+1)//2)*2:
            continue
        else:
            print(0)
            break
    else:
        print(pow(2,(n-1)//2,mod))

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

print(ans)

Solution (Python):

import sys
input = sys.stdin.readline


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

C = dict(Counter(A))

ans = 1
if N%2==0:
    for i in range(N//2):
        if C.get(i*2+1) == 2:
            ans *= 2
            ans %= mod
        else:
            ans = 0
            break
else:
    if C[0] == 1:
        for i in range(N//2):
            if C.get(i*2+2) == 2:
                ans *= 2
                ans %= mod
            else:
                ans = 0
                break
    else:
        ans = 0

print(ans)

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

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

Solution (Python):
MOD=1000000007
N=int(input())
a=[int(_) for _ in input().split()]
cnt=[0]*N
if N%2==0:
    for i in range(N):
        cnt[a[i]]+=1
    f=True
    for i in range(N):
        if i%2==0 and cnt[i]!=0:
            f=False
        elif i%2==1 and cnt[i]!=2:
            f=False
    if f:
        res=1
        for i in range(N//2):
            res=(res*2)%MOD
        print(res)
    else:
        print(0)
elif N%2==1:
    for i in range(N):
        cnt[a[i]]+=1
    f=True
    for i in range(N):
        if i==0 and cnt[i]!=1:
            f=False
        elif i!=0 and i%2==0 and cnt[i]!=2:
            f=False
        elif i%2==1 and cnt[i]!=0:
            f=False
    if f:
        res=1
        for i in range((N-1)//2):
            res=(res*2)%MOD
        print(res)
    else:
        print(0)

Solution (Python):
def examC(mod):
    N = I()
    A = LI()
    num = (N+1)%2
    loop = (N+1)//2
    cur = int(1)
    L = [0]*loop
    if num==0:
        L[0] +=1
    for i in range(N):
        L[A[i]//2] += 1
        if L[A[i]//2]>=3:
            cur = int(0)
            break
    for _ in range(N//2):
        cur = (cur*2)%mod
    print(cur)





import sys
from collections import Counter,defaultdict,deque
def I(): return int(sys.stdin.readline())
def LI(): return list(map(int,sys.stdin.readline().split()))
def LS(): return sys.stdin.readline().split()
def S(): return sys.stdin.readline().strip()
mod = 10**9 + 7
inf = float('inf')

examC(mod)

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

mod = 10**9 + 7

b = set(a)

if n%2==0:
    check = len([ i for i in a if i%2==1 ])
    if check==n and len(b)==(n//2):
        ans = 2**(n//2) % mod
        print(ans)
        exit()
    else:
        print(0)
        exit()
else:
    check = len([ i for i in a if i%2==0 ])
    if check==n and len(b)==((n+1)//2) and a.count(0)==1:
        ans = 2**((n-1)//2) % mod
        print(ans)
        exit()
    else:
        print(0)
        exit()

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

if N%2==1:
    check = [1] + [2]*N
else:
    check = [2] + [2]*N
    
for i in box:
    check[i] -= 1

cnt = 0

for i in box:
    if check[i] == 0:
        cnt += 1
    else:
        print(0)
        break

if cnt == len(box):
    print(2**(N//2)%(10**9+7))

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

n = int(input())
a = list(map(int, input().split()))
if n%2==0:
    p = [0]*(n//2)
    for i in range(n):
        x = (a[i]-1)//2
        p[x]+=1
    m = len(p)
    for i in range(m):
        if p[i]!=2:
            print(0)
            exit()
    ans = (2**m)%INF
    print(ans)
else:
    p = [0]*(((n-1)//2)+1)
    for i in range(n):
        x = a[i]//2
        p[x]+=1
    m = len(p)
    if p[0]!=1:
        print(0)
        exit()
    for i in range(1,m):
        if p[i]!=2:
            print(0)
            exit()
    m -=1
    ans = (2**m)%INF
    print(ans)

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

def out_detect(n,L):
  flag = 0
  if n%2 == 0:
    for i in range(n):
      if L[i] != -(-(i+1)//2)*2-1:
        flag = 1
        break
  else:
    if L[0] != 0:
      flag = 1
      return (flag)
    for i in range(1,n):
      if L[i] != (-(-i//2)*2):
        flag = 1
        break
  return (flag)

if out_detect(n,L) == 1:
  print(0)
else:
  if n%2 == 0:
    out = pow(2,n//2)
  else:
    out = pow(2,(n-1)//2)
  print(out%(pow(10,9)+7))

Solution (Python):
from collections import defaultdict

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

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

if N % 2 == 0:
    for i in range(1, N // 2 + 1):
        if d[2 * i - 1] == 2:
            d[2 * i - 1] = 0
else:
    for i in range(1, N // 2 + 1):
        if d[2 * i] == 2:
            d[2 * i] = 0
    if d[0] == 1:
        d[0] = 0
if sum(d.values()) != 0:
        print(0)
else:
    print(2 ** (N // 2) % (10**9 + 7))

Solution (Python):
n = int(input())
A = list(map(int, input().split()))
set_A = set(A)

ans = 1

if n%2==0:
  if n//2 != len(set(A)):
    ans = 0
else:
  if A.count(0)!=1:
    ans = 0
  
  set_A.remove(0)
  if (n-1)//2 != len(set_A):
    ans = 0
      
if ans!=0:
  ans = 2**(len(set_A))

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

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
A.sort()
n=N//2
MOD=10**9+7
ans=(2**n)%MOD

import sys
if N==1:
    print(1)
    sys.exit()

f=1
if N%2==1:
    for i in range(N):
        if A[i] != 2*(-(-i//2)):
            f=0
            break
else:
    for i in range(N):
        if A[i] != 1+(i//2)*2:
            f=0
            break

print([0,ans][f])

Solution (Python):
INF = int(1e9+7)


def main():
    N, *An = map(int, open(0).read().split())
    An.sort()
    if N % 2:
        if [0] + [i for i in range(2, N, 2) for j in range(2)] == An:
            print(2 ** (N // 2) % INF)
            return
    else:
        if [i for i in range(1, N, 2) for j in range(2)] == An:
            print(2 ** (N // 2) % INF)
            return
    print(0)
    return


main()

Solution (Python):
from functools import reduce
INF = int(1e9+7)


def main():
    N, *An = map(int, open(0).read().split())
    An.sort()
    if N % 2:
        if [0] + [i for i in range(2, N, 2) for j in range(2)] == An:
            print(reduce(lambda x, y: (x << 1) % INF, range(N // 2), 1))
            return
    else:
        if [i for i in range(1, N, 2) for j in range(2)] == An:
            print(reduce(lambda x, y: (x << 1) % INF, range(N // 2), 1))
            return
    print(0)
    return


main()

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

if n%2 == 0:
    for i in range(n):
        if A[i] != (i//2)*2+1:
            print(0)
            break
    else: print(2**(n//2)%1000000007)

else:
    for i in range(n):
        if A[i] != ((i+1)//2)*2:
            print(0)
            break
    else: print(2**(n//2)%1000000007)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
A.sort()
if N == 1:
    print(1)
    exit(0)

elif N % 2 == 0:
    for i in range(0,N//2+1,2):
        if A[i] == A[i+1]:
            continue
        else:
            print(0)
            exit(0)
else:
    for i in range(1,N//2+2,2):
        if A[i] == A[i+1]:
            continue
        else:
            print(0)
            exit(0)
print(2**(N//2)%(10**9+7))

Solution (Python):
MOD = 1000000007
n = int(input())
l = list(map(int,input().split()))
a = {}
for i in l:
    if i in a:
        a[i] += 1
    else:
        a[i] = 1

cur = 1 if n % 2 == 0 else 0

ok = True
while cur < n:
    x = 1 if cur == 0 else 2
    if not cur in a or a[cur] != x:
        ok = False
        break
    cur += 2

ans = 0
if ok:
    ans = 1
    for _ in range(n // 2):
        ans = ans * 2 % MOD

print(ans)