Problem:
 Score : 300 points    Problem Statement There are N people, conveniently numbered 1 through N .
They were standing in a row yesterday, but now they are unsure of the order in which they were standing.
However, each person remembered the following fact: the absolute difference of the number of the people who were standing to the left of that person, and the number of the people who were standing to the right of that person.
According to their reports, the difference above for person i is A_i .  Based on these reports, find the number of the possible orders in which they were standing.
Since it can be extremely large, print the answer modulo 10^9+7 .
Note that the reports may be incorrect and thus there may be no consistent order.
In such a case, print 0 .      Constraints  1≦N≦10^5  0≦A_i≦N-1         Input The input is given from Standard Input in the following format:  N  A_1  A_2  ...  A_N       Output Print the number of the possible orders in which they were standing, modulo 10^9+7 .        Sample Input 1 5
2 4 4 0 2      Sample Output 1 4  There are four possible orders, as follows:   2,1,4,5,3  2,5,4,1,3  3,1,4,5,2  3,5,4,1,2        Sample Input 2 7
6 4 0 2 4 0 2      Sample Output 2 0  Any order would be inconsistent with the reports, thus the answer is 0 .       Sample Input 3 8
7 5 1 1 7 3 5 3      Sample Output 3 16

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

from collections import Counter

class Mint:
    
    MOD = 10**9+7
    
    def __init__(self, x=0):
        self.x = (x%self.MOD + self.MOD) % self.MOD
    
    def __iadd__(self, other):
        self.x += other.x
        if self.x >= self.MOD:
            self.x -= self.MOD
        return self
    
    def __isub__(self, other):
        self.x += self.MOD - other.x
        if (self.x >= self.MOD):
            self.x -= self.MOD
        return self
    
    def __imul__(self, other):
        self.x *= other.x
        self.x %= self.MOD;
        return self;
    
    def __add__(self, other):
        ans = Mint(self.x)
        ans += other
        return ans
        
    def __sub__(self, other):
        ans = Mint(self.x)
        ans -= other
        return ans
    
    def __mul__(self, other):
        ans = Mint(self.x)
        ans *= other
        return ans
    
    def __pow__(self, n):
        if n == 0:
            return Mint(1)
        a = self.__pow__(n >> 1)
        a *= a
        if n&1:
            a *= self
        return a
    
    def inv(self):
        return self**(self.MOD-2)
    
    def __ifloordiv__(self, other):
        self *= other.inv()
        return self
    
    def __floordiv__(self, other):
        ans = Mint(self.x)
        ans //= other
        return ans
        
    

def Main(N, A):
    counter = Counter(A)
    if len(A)%2 == 0:
        v = counter.values()
        s = set(v)
        if len(s) > 1:
            return 0
        else:
            k = list(counter.keys())
            k.sort()
            for i, e in enumerate(k):
                if e != 2*i+1:
                    return 0
            return (Mint(2)**(len(A)//2)).x
    else:
        if 0 not in counter:
            return 0
        if 0 in counter and counter[0] != 1:
            return 0
        del counter[0]
        v = counter.values()
        s = set(v)
        if len(s) > 1:
            return 0
        else:
            k = list(counter.keys())
            k.sort()
            for i, e in enumerate(k):
                if e != 2*(i+1):
                    return 0
            return (Mint(2)**(len(A)//2)).x           
                    
                

res = Main(N, A)
print(res)

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

print(2**(n//2)%1000000007 if flg else 0)

Solution (Python):
n = int(input())
l = list(map(int,input().split()))
s = set(l)

if sum(l) == 2 * sum(s):
  flg = True
else:
  flg = False

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

Solution (Python):
def main():
    from collections import Counter
    n, *a = map(int, open(0).read().split())
    c = Counter(a)
    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
    ans = 2 ** (n // 2) % 1000000007 if f is True else 0
    print(ans)


if __name__ == '__main__':
    main()

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):
def pow_mod(n, k, m):
    if k == 0:
        return 1
    if k & 1:
        return (pow_mod(n, k - 1, m) * n % m) % m
    else:
        return (pow_mod(n, k // 2, m) ** 2) % m

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

Solution (Python):
N = int(input())
A = sorted(map(int, input().split()))
print(pow(2, N >> 1, 10 ** 9 + 7) if (N & 1 and sorted(list(range(0, N, 2)) + list(range(2, N, 2))) == A) or (not N & 1 and sorted(list(range(1, N, 2)) + list(range(1, N, 2))) == A) else 0)

Solution (Python):
n = int(input())
cnts = [0]*n
alist = list(map(int,input().split()))
mod = 10**9+7

for i in range(n):
    cnts[alist[i]] += 1

p = n%2
if p == 1:
    cnts[0] += 1

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

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

if N%2 == 0:
  B = list(range(N-1,0,-2))+list(range(1,N,2))
else:
  B = list(range(N-1,0,-2))+list(range(0,N,2))

if Counter(A) != Counter(B):
  print(0)
else:
  mod = 10**9+7
  print(2**(N//2)%mod)

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

Solution (Python):
import sys
import itertools
sys.setrecursionlimit(1000000000)
from heapq import heapify,heappop,heappush,heappushpop
import math
import collections
MOD = 10**9+7
n = int(input())
a = list(map(int,input().split()))

if n%2 == 0:
    c = collections.Counter(a)
    item = []
    for key,value in c.items():
        item.append([key,value])
    item.sort()
    ans = 1
    for i in range(len(item)):
        if 2*i + 1 == item[i][0]:
            if item[i][1] == 2:
                ans *= 2
                ans %=MOD
            else:
                print(0)
                sys.exit()
        else:
            print(0)
            sys.exit()
    print(ans%MOD)
else:
    c = collections.Counter(a)
    ans = 1
    item = []
    for key,value in c.items():
        item.append([key,value])
    item.sort()
    for i in range(1,len(item)):
        if 2*i == item[i][0]:
            if item[i][1] == 2:
                ans *= 2
                ans %=MOD
            else:
                print(0)
                sys.exit()
        else:
            print(0)
            sys.exit()
    if item[0][0] == 0 and item[0][1] == 1:
        print(ans%MOD)
    else:
        print(0)

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

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

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

Solution (Python):
def main():
  n=int(input())
  a=sorted(list(map(int,input().split())))
  mod=pow(10,9)+7
  if n%2==0:
    b=[2*(i//2)+1 for i in range(n)]
    if  not all(a[i]==b[i] for i in range(n)):
      ans=0
    else:
      ans=pow(2,n//2,mod)
  else:
    b=[0]+[2*(i//2) for i in range(2,n+1)]
    if not all(a[i]==b[i] for i in range(n)):
      ans=0
    else:
      ans=pow(2,n//2,mod)
  print(ans)
if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter
n = int(input())
A = list(map(int,input().split()))
mod = 10**9 + 7
c = Counter(A)
flg = True
for k,v in c.items():
    if k==0:
        if v!=1:
            flg = False
    else:
        if v!=2:
            flg = False
if flg is False:
    print(0)
else:
    print(pow(2, n//2, mod))

Solution (Python):
from collections import Counter

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


if N % 2 == 0:
    for key, value in c.items():
        if key % 2 != 1:
            print(0)
            exit()
        if value != 2:
            print(0)
            exit()
else:
    if c.get(0) is None:
        print(0)
        exit()
    for key, value in c.items():
        if key == 0:
            continue
        if key % 2 != 0:
            print(0)
            exit()
        if value != 2:
            print(0)
            exit()
ans = pow(2, N // 2, MOD)
print(ans)

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

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

li=[]

for i in range(n-1,-(n),-2):
    li.append(abs(i))

li.sort()

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

Solution (Python):
import collections
def solve(n, a_list):

    count = collections.Counter()
    for a in a_list:
        count[a] += 1

    count[0] += 1
    c = [False] * n
    for k, v in count.items():
        c[k] = (v == 2)

    if n % 2 == 1:
        tmp = all([v for i, v in enumerate(c) if i % 2 == 0])
    else:
        tmp = all([v for i, v in enumerate(c) if i % 2 == 1])

    if tmp:
        return (2 ** (n//2) ) % (10**9+7)
    else:
        return 0

if __name__ == "__main__":
    n = int(input())
    a_list = [int(i) for i in input().split()]
    print(solve(n, a_list))

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

flg = True
if N%2 == 0:
  for i in range(0, N//2): flg &= A[2*i] == A[2*i+1] == 2*i+1
else:
  flg &= A[0] == 0
  for i in range(1, (N+1)//2): flg &= A[2*i-1] == A[2*i] == 2*i

def modpow(n, r, m):
  if r == 0: return 1
  if r%2 == 0: return modpow(n, r//2, m)**2 % m
  return n * modpow(n, r-1, m) % m

print(modpow(2, N//2, 10**9+7) if flg else 0)

Solution (Python):
from collections import Counter

N = int(input())
lst = [int(x) for x in input().split()]
counter = Counter(lst)

if N % 2 == 0:
    if len(counter) * 2 != N:
        print(0)
        exit()
    for x in range(1, N, 2):
        if counter[x] != 2:
            print(0)
            exit()

else:
    if len(counter) * 2 - 1 != N:
        print(0)
        exit()
    if counter[0] != 1:
        print(0)
        exit()
    for x in range(2, N + 1, 2):
        if counter[x] != 2:
            print(0)
            exit()

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

Solution (Python):
from collections import Counter

n = int(input())
a = list(map(int,input().split()))
c = Counter(a)
m = c.most_common()
judge = 0
ans = 1
if n%2 == 0:
    for i in range(len(m)):
        if m[i][0]%2==0 or m[i][1]!=2 or m[i][0]>n-1:
            judge = 1
    num=n//2
else:
    for i in range(len(m)):
        if (m[i][0]==0 and m[i][1]!=1) or m[i][0]%2==1 or (m[i][1]!=2 and m[i][0]!=0)or m[i][0]>n-1:
            judge = 1
    num=(n-1)//2
if judge ==1:
    print('0')
else:
    for i in range(num):
        ans=ans*2%1000000007
    print(ans)

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

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

alist.sort()



mod = (10**9 + 7)

if N % 2 == 1:
    alist.pop(0)
    for i in range(N//2):
        
        if alist[i*2] != 2*(i + 1) or alist[i*2 + 1] != 2*(i + 1):
            print(0)
            exit(0)
    print(2**(N//2)%mod)
else:
    for i in range(N//2):
        
        if alist[i*2] != 2*i + 1 or alist[i*2 + 1] != 2*i + 1:
            print(0)
            exit(0)
    print(2**(N//2)%mod)

Solution (Python):
N = int(input())
A = [int(i) for i in input().split()]
a = [0] * ((N + 1) // 2)
for i in A:
	if N % 2:
		if i % 2:
			print(0)
			exit()
	else:
		if i % 2 == 0:
			print(0)
			exit()
	a[i // 2] += 1
if N % 2:
	if any(i != 2 for i in a[1:]) or a[0] != 1:
		print(0)
		exit()
else:
	if any(i != 2 for i in a):
		print(0)
		exit()
print(2 ** (N // 2) % 1000000007)

Solution (Python):
n = int(input())
s = list(map(int, input().split()))
s_set = set(s)
count = 2 ** ((n) // 2)
if (sum(s) == 2 * sum(s_set)):
    print(count % (10 ** 9 + 7))
else:
    print(0)

Solution (Python):
def resolve():
    N = int(input())
    
    A = input().split() 
    import collections
    counter = collections.Counter(A)
    if N % 2 == 1:
        if counter["0"] != 1:
            print("0")
            return
        for k, v in counter.items():
            if k == "0":
                continue
            if int(k) % 2 == 1:
                print("0")
                return
            if v != 2:
                print("0")
                return
    else:
        for k, v in counter.items():
            if int(k) % 2 == 0:
                print("0")
                return
            if v != 2:
                print("0")
                return
    
    print( (2**(N//2)) % (10**9+7) )




if '__main__' == __name__:
    resolve()

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

def resolve():
    N = int(input())
    
    
    A = input().split()
    import collections
    counter = collections.Counter(A)
    if N % 2 == 1:
        if counter["0"] != 1:
            print("0")
            return
        for k, v in counter.items():
            if k == "0":
                continue
            if int(k) % 2 == 1:
                print("0")
                return
            if v != 2:
                print("0")
                return
    else:
        for k, v in counter.items():
            if int(k) % 2 == 0:
                print("0")
                return
            if v != 2:
                print("0")
                return
    
    print( (2**(N//2)) % (10**9+7) )




if '__main__' == __name__:
    resolve()

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

def resolve():
    N = int(input())
    
    A = readline().rstrip().split()
    import collections
    counter = collections.Counter(A)
    if N % 2 == 1:
        if counter["0"] != 1:
            print("0")
            return
        for k, v in counter.items():
            if k == "0":
                continue
            if int(k) % 2 == 1:
                print("0")
                return
            if v != 2:
                print("0")
                return
    else:
        for k, v in counter.items():
            if int(k) % 2 == 0:
                print("0")
                return
            if v != 2:
                print("0")
                return
    
    print( (2**(N//2)) % (10**9+7) )




if '__main__' == __name__:
    resolve()

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

if A != B:
  print(0)
else:
  if N % 2 == 0:
    print(pow(2, N//2, mod))
  else:
    print(pow(2, (N-1)//2, mod))

Solution (Python):
n = int(input())
q = [int(x) for x in input().split(' ')]
q_set = set(q)

if (n%2 == 1):
    count = 2**((n-1)//2)
else:
    count = 2**(n//2)
    
    
if (sum(q) == 2*sum(q_set)):
    print(count%(10**9+7))
else:
    print(0)

Solution (Python):
import sys
readline = sys.stdin.readline
from collections import Counter
MOD = 10 ** 9 + 7

def main():
    N = int(readline())
    A = list(map(int, readline().rstrip().split()))
    c = Counter(A)
    if N % 2 == 1:
        if c[0] != 1:
            print(0)
            return
        for i in range(2, N, 2):
            if c[i] != 2:
                print(0)
                return

    else:
        for i in range(1, N, 2):
            if c[i] != 2:
                print(0)
                return

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

if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter
N = int(input())
A = [int(c) for c in input().split()]
ans = 1
MOD = 10**9+7
Cnt = Counter(A)
if N%2==1:
  for k,v in Cnt.items():
    if (k%2==0 and v==2) or (k==0 and v==1):
      ans *= v
      ans %= MOD
    else:
      print(0)
      break
  else:
    print(ans)
else:
  for k,v in Cnt.items():
    if k%2==1 and v==2:
      ans *= v
      ans %= MOD
    else:
      print(0)
      break
  else:
    print(ans)

Solution (Python):
n = int(input())
a_ls = list(map(int, input().split()))
mod = 1000000007
isOK = True
if n % 2 == 0:
    count_ls = [0] * n
    for a in a_ls:  
        count_ls[a] += 1
    suppose = [0,2] * (n//2)
    if not count_ls == [0,2] * (n//2):
        isOK = False
else:
    count_ls = [0] * n
    for a in a_ls:  
        count_ls[a] += 1
    suppose = [1] + [0,2] * (n//2)
    if not count_ls == suppose:
        isOK = False
if isOK:
    ans = (2 ** (n // 2)) % mod
else:
    ans = 0
print(ans)

Solution (Python):
import collections

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

c = collections.Counter(l)
ans = 0
flag = True
if N%2==0:
    for i in range(1,N+1,2):
        if c[i] != 2:
            flag = False
else:
    for i in range(0,N+1,2):
        if i == 0 and c[i] != 1:
            flag = False 
        if i != 0 and c[i] != 2: 
            flag = False

if flag:
    ans = 2**int(N/2)
print(ans % (10**9+7))

Solution (Python):
from collections import Counter

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

count = Counter(Alist)
res = 1
if N % 2 ==0:
    for i in range(1,N,2):
        if count[i] != 2:
            print(0)
            exit()
else:
    if count[0] != 1:
        print(0)
        exit()
    else:
        for i in range(2,N,2):
            if count[i] != 2:
                print(0)
                exit()
print(2**(N//2) % (10**9+7))

Solution (Python):
from collections import defaultdict

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

for i in range(n):
    cnt[a[i]] += 1
flag = True

if 0 in cnt.keys():
    del cnt[0]

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

Solution (Python):
from collections import Counter
n=int(input())
a=list(map(int,input().split()))
b=Counter(a)
c=len(([i[0] for i in b.items() if i[1] == 2]))
if n%2==0:
    if n//2==c:
        print(2**(len(set(a)))%1000000007)
    else:
        print(0)
else:
    if (n-1)//2==c and a.count(0)==1:
        print(2**(len(set(a))-1)%1000000007)
    else:
        print(0)

Solution (Python):

import math
import fractions
import bisect
import collections
import itertools
import heapq
import string
import sys
import copy
from decimal import *
from collections import deque
sys.setrecursionlimit(10**7)
MOD = 10**9+7
INF = float('inf') 
def gcd(a,b):return fractions.gcd(a,b) 
def lcm(a,b):return (a*b) // fractions.gcd(a,b) 
def iin(): return int(sys.stdin.readline()) 
def ifn(): return float(sys.stdin.readline()) 
def isn(): return sys.stdin.readline().split() 
def imn(): return map(int, sys.stdin.readline().split()) 
def imnn(): return map(lambda x:int(x)-1, sys.stdin.readline().split()) 
def fmn(): return map(float, sys.stdin.readline().split()) 
def iln(): return list(map(int, sys.stdin.readline().split())) 
def iln_s(): return sorted(iln()) 
def iln_r(): return sorted(iln(), reverse=True) 
def fln(): return list(map(float, sys.stdin.readline().split())) 
def join(l, s=''): return s.join(l) 
def perm(l, n): return itertools.permutations(l, n) 
def perm_count(n, r): return math.factorial(n) // math.factorial(n-r) 
def comb(l, n): return itertools.combinations(l, n) 
def comb_count(n, r): return math.factorial(n) // (math.factorial(n-r) * math.factorial(r)) 
def two_distance(a, b, c, d): return ((c-a)**2 + (d-b)**2)**.5 
def m_add(a,b): return (a+b) % MOD
def lprint(l): print(*l, sep='\n')

N = iin()
A = iln()

counter = dict()

possible = True
for a in A:
    if a in counter:
        counter[a] += 1
        if a == 0 and counter[a] > 1:
            possible = False
        elif a != 0 and counter[a] > 2:
            possible = False
    else:
        counter[a] = 1
if possible:
    print(2**(N//2)%MOD)
else:
    print(0)

Solution (Python):
def abc050_c():
  n = int(input())
  A = list(map(int, input().split()))
  div = 10**9 + 7

  from collections import Counter
  cntr = Counter(A)

  if n % 2 == 0:
    
    for i in range(1, n, 2):
      if cntr[i] != 2:
        print(0)
        return
  else:
    
    if cntr[0] != 1:
      print(0)
      return
    for i in range(2, n, 2):
      if cntr[i] != 2:
        print(0)
        return

  
  
  ans = pow(2, n//2, div)
  print(ans)

abc050_c()

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

mod = 10**9+7
c = collections.Counter(a)
c =c.most_common()
c.sort()

if n%2==0:
    for i in range(len(c)):
        if c[i][0]==i*2+1 and c[i][1]==2:
            continue
        else:
            print(0)
            exit()
    ans=pow(2,n//2,mod)
    print(ans)

else:
    for i in range(len(c)):
        if i==0:
            if c[i][0]==0 and c[i][1]==1:
                continue
            else:
                print(0)
                exit()
        else:
            if c[i][0] == i * 2 and c[i][1] == 2:
                continue
            else:
                print(0)
                exit()
    ans=pow(2,n//2,mod)
    print(ans)

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

Solution (Python):
from collections import Counter
def main():
  N = int(input())
  A = [int(_) for _ in input().split()]
  MOD = 10 ** 9 + 7
  B = Counter(A)
  
  if N%2 == 0:
    for i in range(N):
      if (i%2 == 0 and B[i] == 0) or (i%2 == 1 and B[i] == 2):
        pass
      else:
        print(0)
        break
    else:
      print(pow(2, N//2, MOD))
  else:
    for i in range(N):
      if (i == 0 and B[i] == 1) or (i%2 == 0 and B[i] == 2) or (i%2 == 1 and B[i] == 0):
        pass
      else:
        print(0)
        break
    else:
      print(pow(2, N//2, MOD))
      
  return

if __name__ == '__main__':
  main()

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

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

yn=""
if n%2==0:
    for i in range(n):
        if i%2==0:
            if icnt[i]!=0:
                yn="NO"
                break
        else:
            if icnt[i]!=2:
                yn="NO"
                break
else:
    for i in range(n):
        if i==0:
            if icnt[i]!=1:
                yn="NO"
                break
        elif i%2==0:
            if icnt[i]!=2:
                yn="NO"
                break
        else:
            if icnt[i]!=0:
                yn="NO"
                break
if yn=="NO":
    print(0)
else:
    n2=n//2
    p=10**9+7
    print(pow(2,n2,p))

Solution (Python):
from collections import Counter
n = int(input())
list_A = list(map(int, input().split()))
mod = pow(10, 9) + 7

list_Counter = list(Counter(list_A).items())
ans = 1
list_Counter.sort(key=lambda x:x[0])

if n % 2 == 0:
    for i in range(n//2):
        l = list_Counter[i]
        if l[0] != 2*i + 1 or l[1] != 2:
            ans = -1

    if ans == -1:
        print(0)
    else:
        print((2**(n//2))%mod)
else:
    if list_Counter[0][0] == 0 and list_Counter[0][1] == 1:
        for i in range(1, n//2+1):
            l = list_Counter[i]
            if l[0] != 2*i or l[1] != 2:
                ans = -1
    else:
        ans = -1

    if ans == -1:
        print(0)
    else:
        print((2**(n//2))%mod)

Solution (Python):
from collections import Counter


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

C = Counter(A)

isAble = True
k = N - 1
while k >= 0:
    if k == 0:
        if C[k] != 1:
            isAble = False
    else:
        if C[k] != 2:
            isAble = False
    k -= 2

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

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

if sorted(a)!=b:
  ans=0
else:
  ans=2**(n//2)
print(ans%(10**9+7))

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

Solution (Python):


from collections import Counter


def main():

    N = int(input())
    A = list(map(int, input().split()))
    arr = [abs(i - (N - i - 1)) for i in range(N)]
    result = 0
    mod = 10**9 + 7

    if Counter(A) == Counter(arr):
        result = (2**(N // 2)) % mod

    print(result)


if __name__ == "__main__":
    main()

Solution (Python):
import io

data = int(input())
array = list(map(int,input().split()))
array.sort()
modulus = 10**9 + 7
result = (2 ** (data // 2)) % modulus
array2 = []
for i in range(data):
  array2 += [abs(data+1-2*(i+1))]
array2.sort()
if array == array2 :
  print(result)
else:
  print(0)

Solution (Python):
N = int(input())
nums = [int(e) for e in input().split()]
nums.sort()
t=1
ans = 1
t = 10**9
t+=7
i=1
k=0
if(N%2)==1:
    if(nums.count(0) == 1):
        while(i<N):
            if nums[i] == nums[i+1]:
                i+=2
                ans = (ans *2)%t
                continue
            else:
                print('0')
                break
        else:
            print(ans)
    else:
        print('0')
else:
    while(k<N):
        if nums[k] == nums[k+1]:
            k += 2
            ans = (ans * 2)%t
            continue
        else:
            print('0')
            break
    else:
        print(ans)

Solution (Python):
N = int(input())
o, h = N%2, N//2
arr = [0]*h
for a in map(int, input().split()):
    if a > 0:
        arr[a//2 - o] += 1
if all(c == 2 for c in arr):
    print((1 << h) % (10**9 + 7))
else:
    print(0)

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
d = {}
for i in a:
  if ((i+n)%2 == 0) and (i != 0):
    print(0)
    exit()
  if i in d:
    d[i] += 1
    if (d[i] == 3) or (i == 0):
      print(0)
      exit()
  else:
    d[i] = 1
ans = 1
for i in list(d.values()):
  ans *= i
print(ans%1000000007)

Solution (Python):
n = int(input())
l = list(map(int,input().split()))
s = 1
if n%2!=0:
  if l.count(0)!=1:
    s =0
  else:
    l.remove(0)
    if len(set(l))==(n-1)//2:
      s = 2**((n-1)//2)
    else:
      s =0
else:
    if len(set(l))==n//2:
      s = 2**(n//2)
    else:
      s = 0
print(int(s)%(10**9+7))

Solution (Python):
n,*a=map(int,open(0).read().split())
a=sorted(a)
cnt=0
if len(a)%2==0:
  for i in range(1,len(a),2):
    if [i,i]==a[i-1:i+1]:
      cnt+=1
    else:
      cnt=-10**5-1
else:
  if a[0]==0:
    for i in range(2,len(a),2):
      if [i,i]==a[i-1:i+1]:
        cnt+=1
      else:
        cnt=-10**5-1
  else:
    cnt=-10**5-1
print((2**cnt)%(10**9+7) if cnt>=0 else 0)

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

from collections import Counter
MOD = 10**9 + 7
c = Counter(a)

ans = 0

if n % 2 == 1:
    for i in range(2, n, 2):
        if c[i] != 2:
            print(0)
            exit()
    if c[0] == 1:
        ans = pow(2, n // 2, MOD)
else:
    for i in range(1, n, 2):
        if c[i] != 2:
            print(0)
            exit()
    ans = pow(2, n // 2, MOD)
print(ans)

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

from collections import Counter
MOD = 10**9 + 7
c = Counter(a)

ans = 0

if n % 2 == 1:
    for i in range(2, n, 2):
        if c[i] != 2:
            print(0)
            exit()
    if c[0] == 1:
        ans = pow(2, n // 2, MOD)
else:
    for i in range(1, n, 2):
        if c[i] != 2:
            print(0)
            exit()
    ans = pow(2, n // 2, MOD)
print(ans)

Solution (Python):
N = int(input())
A = list(map(int,input().split()))
A.sort()
import sys, copy, math, heapq, bisect
from itertools import accumulate
from collections import deque, defaultdict, Counter
input = sys.stdin.readline 
sys.setrecursionlimit(500000)
mod = 10**9+7
D = Counter(A)
if N%2==0:
    ans = 1
    for i,k in enumerate(D.keys()):
        if D[k]==2:
            ans = ans*2%mod
        else:
            ans = 0
            break
    print(ans)


else:
    ans = 1
    for i,k in enumerate(D.keys()):
        if i==0 and D[k]==1:
            continue
        elif i==0:
            ans = 0
            break
        elif D[k]==2:
            ans = ans*2%mod
        else:
            ans = 0
            break
    print(ans)

Solution (Python):

import math
import heapq
import bisect
from collections import Counter, deque
import itertools


MOD = 10**9+7

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

c = sorted(list(Counter(A).items()))

ans = 1
if N%2 == 1:
    for i in range(len(c)):
        if i==0:
            if c[i][0] == 0 and c[i][1] == 1:
                ans = 1
            else:
                ans = 0
        else:
            if c[i][0] == i*2 and c[i][1] == 2:
                ans *= 2
                ans %= MOD
            else:
                ans = 0
else:
    for i in range(len(c)):
        if c[i][0] == i*2+1 and c[i][1] == 2:
            ans *= 2
            ans %= MOD
        else:
            ans = 0

print(ans)