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):
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 cur in a and 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)

Solution (Python):
INFTY = 10**9+7
N = int(input())
A = list(map(int,input().split()))
C = {}
for i in range(N):
    if A[i] not in C:
        C[A[i]] = 0
    C[A[i]] += 1
if N%2==0:
    flag = 0
    for i in range(1,N,2):
        if i in C and C[i]==2:
            pass
        else:
            flag = 1
            break
else:
    flag = 0
    for i in range(2,N,2):
        if i in C and C[i]==2:
            pass
        else:
            flag = 1
            break
    if 0 not in C or C[0]!=1:
        flag = 1
cnt = 0
if flag==0:
    cnt = 1
    for i in range(N//2):
        cnt = (cnt*2)%INFTY
print(cnt)

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

if N % 2 != 0:
    if A[0] == 0:
        for i in range(2, N, 2):
            if not (A[i] == i and A[i-1] == i):
                print(0)
                exit()
        order_count = 2 ** ((N - 1) // 2) % mod
    else:
        print(0)
        exit()

else:
    for i in range(1, N, 2):
        if not (A[i] == i and A[i-1] == i):
            print(0)
            exit()
    order_count = 2 ** (N // 2) % mod 

print(order_count)

Solution (Python):

import sys
from collections import Counter
MOD = 1000000007  


def solve(N: int, A: "List[int]"):
    counter = Counter(A)

    if N%2==0:
        for value in counter.values():
            if value%2!=0:
                print(0)
                return 
        
        print(2**(N//2)%MOD)
    else:
        for key,value in counter.items():
            if (value%2!=0 and int(key)!=0) or (value%2==0 and int(key)==0):
                print(0)
                return 
        
        print(2**((N-1)//2)%MOD)

    return


def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    A = [int(next(tokens)) for _ in range(N)]  
    solve(N, A)

if __name__ == '__main__':
    main()

Solution (Python):
n=int(input())
l=list(map(int,input().split()))
d={}
for i in range(n):
  d[i]=0
for i in l:
  d[i]+=1
b=True
if n%2==1:
  if d[0]!=1:
    b=False
  for i in range(1,n//2+1):
    if d[i*2]!=2:
      b=False
else:
  for i in range(n//2):
    if d[i*2+1]!=2:
      b=False
if b:
  print((2**(n//2))%(10**9+7))
else:
  print(0)

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

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

Solution (Python):
from collections import Counter

n=int(input())
a=list(map(int,input().split()))
c=Counter(a)
if (1 in c.values() and c[0]!=1) or 3 in c.values():
    print(0)
else:
    if n%2==0:
        print((2**(n//2))%(10**9+7))
    else:
        print((2**((n-1)//2))%(10**9+7))

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

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

if A == B:
    ans = (2 ** i_max) % (10**9 + 7)
    print(ans)
else:
    print(0)

Solution (Python):


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

if N%2 == 0:
    tmp = []
    tmp2 = 1
    while tmp2 <= N-1:
        tmp.extend([tmp2, tmp2])
        tmp2 += 2
        
    if A != tmp:
        print(0)
    else:
        print((2**(N//2))%(10**9+7))
    
else:
    tmp = [0]
    tmp2 = 2
    while tmp2 <= N-1:
        tmp.extend([tmp2, tmp2])
        tmp2 += 2
        
    if A != tmp:
        print(0)
    else:
        print((2**((N-1)//2))%(10**9+7))

Solution (Python):
n = int(input())
A = list(map(int,input().split()))
nums = {}
nums2 = {}
mod = 10**9 +7
for i in range(1,n+1):
    left = i -1
    right = n -i
    a = abs(left - right)
    if a in nums:
        nums[a] +=1
    else:
        nums[a] = 1

for a in A:
    if a in nums2:
        nums2[a] +=1
    else:
        nums2[a] = 1

if nums==nums2:
    if n%2==1:
        print(2**(len(nums)-1)%mod)
    else:
        print(2**(len(nums))%mod)
else:
    print(0)

Solution (Python):
N = int(input().strip())
A = list(map(int, input().strip().split(' ')))
if N % 2 == 1:
  checklist = {0:1}
  for i in range((N-1)//2):
    checklist[(i+1)*2] = 2
else:
  checklist = {(i*2+1):2 for i in range(N//2)}

for a in A:
  if a in checklist and checklist[a] in {1,2}:
    checklist[a] -= 1
  else:
    print(0)
    exit()
print(int(2**(N//2))%1000000007)

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


opt = {}
for i in range(N):
  a = abs((N-i-1)-i)
  if a not in opt :
    opt[a] = 1
  else :
    opt[a] += 1 
for i in range(N):
  if A[i] not in opt or opt[A[i]] == 0 :
    print(0)
    exit()
  else:
    opt[A[i]] -= 1 
ans = (2**(N//2))%mod
print(ans)

Solution (Python):
def exp(n):
    if n == 0:
        return 1
    elif n == 1:
        return 2
    if n % 2 == 0:
        tmp = exp(n // 2) % 1000000007
        return (tmp * tmp) % 1000000007
    else:
        tmp = exp(n // 2) % 1000000007
        return (2 * tmp * tmp) % 1000000007
n = int(input())
ar = list(map(int, input().split()))
ar.sort()
if n % 2 == 0:
    curr = 1
    valid = True
    for i in range(1, n, 2):
        if ar[i] == ar[i - 1] == curr:
            curr += 2
            continue
        else:
            valid = False
            break
    if valid:
        print(exp(n // 2))
    else:
        print(0)
else:
    curr = 2
    valid = True
    if ar[0] != 0:
        valid = False
    else:
        for i in range(2, n, 2):
            if ar[i] == ar[i-1] == curr:
                curr += 2
                continue
            else:
                valid = False
                break
    if valid:
        print(exp(n // 2))
    else:
        print(0)

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

counter = collections.Counter(a)
ans = 1
for k, v in counter.items():
    if k != 0:
        if v == 2:
            ans *= 2
        if v == 1:
            ans = 0
            break
print(ans % (10**9 + 7))

Solution (Python):
from functools import reduce

if __name__ == "__main__":
    n = int(input())
    a = [int(x) for x in input().split()]
    x = [0]*n
    """if n % 2 == 0:
        for i in a:
            if i % 2 != 1:
                print(0)
                exit()
    else:
        for i in a:
            if i % 2 != 0:
                print(0)
                exit()"""
    for i in a:
        if i == 0 and x[i] == 1:
            print(0)
            exit()
        elif x[i] == 2:
            print(0)
            exit()
        else:
            x[i] += 1
    print(reduce(lambda x, y: x * y if y != 0 else x, x, 1) % (10 ** 9 + 7))

Solution (Python):
from functools import reduce

if __name__ == "__main__":
    n = int(input())
    a = [int(x) for x in input().split()]
    x = [0]*n
    if n % 2 == 0:
        for i in a:
            if i % 2 != 1:
                print(0)
                exit()
    else:
        for i in a:
            if i % 2 != 0:
                print(0)
                exit()
    for i in a:
        if i == 0 and x[i] == 1:
            print(0)
            exit()
        elif x[i] == 2:
            print(0)
            exit()
        else:
            x[i] += 1
    print(reduce(lambda x, y: x * y if y != 0 else x, x, 1) % (10 ** 9 + 7))

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

Solution (Python):
import sys

stdin = sys.stdin

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

def main():
  n = ni()
  a = na()
  mod = int(1e9+7)

  if n % 2 == 0 and len(set(a)) == n // 2:
    print(2 ** (n // 2) % mod)
  elif n % 2 == 1 and a.count(0) == 1:
    print(2 ** ((n - 1) // 2) % mod)
  else:
    print(0)
main()

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

Solution (Python):
N = int(input().strip())
A = list(map(int, input().strip().split()))
x = N//2

C = [0]*N
for a in A:
    C[a]+=1

if N % 2 == 0:
    for i,c in enumerate(C):
        if i % 2 == 0:
            continue
        if C[i] != 2 :
            print("0")
            exit()
else:
    for i,c in enumerate(C):
        
        if i % 2 == 1:
            continue
        if i == 0:
            if C[i] != 1:
                print("0")
                exit()
            else:
                continue
        elif C[i] != 2 :
            print("0")
            exit()

print((2**x)%int(1.0e9+7))

Solution (Python):


n = int(input())

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

a.sort()
if len(a) %2 == 1:
    odd = True
    now = 0
    if a[0] != 0:
        print(0)
        exit()
    now += 2
    for i in range(1,len(a)//2 + 1 , 2):
        if a[i] != now or a[i+1] != now:
            print(0)
            exit()
        now += 2
        
else:
    odd = False
    now = 1
    for i in range(0,len(a)//2 + 1,2):
        if a[i] != now or a[i+1] != now:
            print(0)
            exit()
        now += 2

print(2**(len(a)//2) %(10**9+7))

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

Solution (Python):
from collections import defaultdict
n = int(input())
a = list(map(int, input().split()))
d = defaultdict(int)
for x in a:
    d[x] += 1
b = [i for i in range(n)[::-1]]
if not all([d[i] == 2, d[i] == 1][n % 2 and i == 0] for i in b[::2]):
    print(0)
else:
    ans = 1
    for v in d.values():
        ans = ans * v % (10**9+7)
    print(ans)

Solution (Python):
from collections import defaultdict
n = int(input())
a = list(map(int, input().split()))
d = defaultdict(int)
for x in a:
    d[x] += 1
b = [i for i in range(n)[::-1]]
e = all(d[i] == 2 if n % 2 == 0 else d[i] ==
        1 if i == 0 else d[i] == 2 for i in b[::2])
if not e:
    print(0)
    exit()
ans = 1
for v in d.values():
    ans = ans * v % (10**9+7)
print(ans)

Solution (Python):
import collections
DIVISOR = 10 ** 9 + 7

def check(n, a_count):
    if n % 2 == 1:
        if set(a_count.keys()) == set(range(0, n, 2)):
            if a_count[0] == 1 and all([a_count[key] == 2 for key in a_count if key != 0]):
                ans = (2 ** (n // 2)) % DIVISOR
                return ans
                
    else:
        if set(a_count.keys()) == set(range(1, n, 2)):
            if all([a_count[key] == 2 for key in a_count]):
                ans = (2 ** (n // 2)) % DIVISOR
                return ans
    return 0


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

a_count = collections.Counter(a)
print(check(n, a_count))

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

ans = 1

for i, v in a.items():
    if i == 0:
        if v != 1:
            print(0)
            exit()
    elif v != 2:
        print(0)
        exit()
    else:
        ans = ans * 2 % (10 ** 9 + 7)
print(ans)

Solution (Python):
import collections as coll
n=int(input())
a=list(map(int,input().split()))
if a.count(0)>1:
    print('0')
    exit()
x=10**9+7
f=0
s=coll.defaultdict(int)
for i in range(n):
    if n%2:
        if a[i]%2: f=1
    else:
        if a[i]%2==0: f=1
    s[a[i]]+=1
    if s[a[i]]>2: f=1
    if f==1:
        print('0')
        exit()
ans=1
for i in range(1,n//2+1): ans=ans*2%x
print(ans)

Solution (Python):
from collections import Counter

N = int(input())
A = list(map(int, input().split()))
a = list(Counter(A).values())
mod = 10 ** 9 + 7

if N % 2 == 0:
    if a.count(2) == N // 2:
        ans = 1
        for i in range(N // 2):
            ans = ans * 2 % mod
        print(ans)
    else:
        print(0)
else:
    if a.count(2) == N // 2 and A.count(0) == 1:
        ans = 1
        for i in range(N // 2):
            ans = ans * 2 % mod
        print(ans)
    else:
        print(0)

Solution (Python):
from collections import Counter
MOD = 1000000007
N = int(input())
A = map(int, input().split())
c = Counter(A)
if N % 2 == 0:
    for i in range(1, N, 2):
        if c[i] != 2:
            print(0)
            exit()
    ans = 2 ** (N // 2) % MOD
else:
    if c[0] != 1:
        print(0)
        exit()
    for i in range(2, N, 2):
        if c[i] != 2:
            print(0)
            exit()
    ans = 2 ** (N // 2) % MOD
print(ans)

Solution (Python):
import collections

n = int(input())
a = list(map(int, input().split()))
li = collections.Counter(a)
key = set(li.keys())
flag = True
mod = (10**9)+7

if n % 2:
    num = set(list(range(0,n,2)))
    if len(key ^ num) != 0:
        flag = False

    for i in li:
        if i == 0 and li[i] != 1:
            flag = False

        elif i != 0 and li[i] != 2:
            flag = False

    if flag:
        print((2**((n-1)//2))%mod)
    else:
        print(0)
else:
    num = set(list(range(1,n,2)))
    if len(key ^ num) != 0:
        flag = False

    for i in li:
        if li[i] != 2:
            flag = False
    if flag:
        print((2**(n//2))%mod)
    else:
        print(0)

Solution (Python):
import collections
n = int(input())
list_a = list(map(int, input().split(" ")))
count = collections.Counter(list_a)

flag = True
for key, value in count.items():
  if value == 2 or (key == 0 and value == 1):
    pass
  else:
    flag = False
    break

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

Solution (Python):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Solution (Python):
n = int(input())
ls = sorted(map(int, input().split()))
MOD = 10**9 + 7
ok = True
if n % 2 == 0:
    for i in range(n // 2):
        i *= 2
        ok = ls[i] == ls[i + 1] == i + 1
        if not ok:
            break
else:
    ok = ls[0] == 0
    for i in range(n // 2):
        i *= 2
        ok = ls[i + 1] == ls[i + 2] == i + 2
        if not ok:
            break
if not ok:
    print(0)
else:
    print(2**(n // 2) % MOD)

Solution (Python):
def main():
  mod=1000000007
  n=int(input())
  a=sorted(list(map(int,input().split())))
  if n%2==0:
    if a==[x//2*2+1 for x in range(n)]:
      print(2**(n//2)%mod)
      return
  else:
    if a==[0]+[x//2*2+2 for x in range(n-1)]:
      print(2**(n//2)%mod)
      return
  print(0)

main()

Solution (Python):
from sys import stdin
from collections import Counter
mod = 10**9+7
N = int(stdin.readline().rstrip())
A = [int(x) for x in stdin.readline().rstrip().split()]
ans = 2**(N//2)
if N % 2 == 0:
    for i in A:
        if i % 2 == 0:
            ans = 0
    for j in Counter(A).values():
        if j != 2:
            ans = 0
else:
    for i in A:
        if i % 2 != 0:
            ans = 0
    for j,k in Counter(A).items():
        if j != 0 and k != 2:
            ans = 0
    if Counter(A)[0] != 1:
        ans = 0
print(ans%mod)

Solution (Python):


from collections import Counter

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

c = Counter(a)
ans = 1
mod = 10 ** 9 + 7
for k, v in c.items():
    if k == 0:
        num = 1
    else:
        num = 2

    if v == num:
        ans *= v
        ans %= mod
    else:
        ans = 0
        break

print(ans)

Solution (Python):
from math import ceil
from collections import Counter

N = int(input())
A = list(map(int, input().split()))
CA = Counter(A)
SCA = sorted(CA.items(), key=lambda x:x[0])

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

if N % 2 == 0:
  for i, j in zip(SCA, range(ceil(N / 2))):
    if not (i[0] == 1 + j * 2 and i[1] == 2):
      print(0)
      exit()
else:
  for i, j in zip(SCA, range(ceil(N / 2))):
    if j == 0:
      if not (i[0] == j * 2 and i[1] == 1 ):
        print(0)
        exit() 
    else:  
      if not (i[0] == j * 2 and i[1] == 2 ):
        print(0)
        exit()
print((2 ** (N // 2)) % (10 ** 9 + 7))

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

Bi = []
if n % 2 == 0:
    half_Bi = list(range(1, n, 2))
    Bi = half_Bi + half_Bi
else:
    half_Bi = list(range(2, n, 2))
    Bi = half_Bi + half_Bi
    Bi.append(0)

A.sort()
Bi.sort()
if A != Bi:
    print(0)
    exit()

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

Solution (Python):
from collections import Counter,defaultdict
import sys,heapq,bisect,math,itertools,string,queue
sys.setrecursionlimit(10**8)
mod = 10**9+7
def inp(): return int(sys.stdin.readline())
def inpl(): return list(map(int, sys.stdin.readline().split()))
def inpl_str(): return list(sys.stdin.readline().split())
def inpln(n): return list(int(sys.stdin.readline()) for i in range(n))

n = inp()
a = inpl()
cnt = Counter(a)
if n%2 == 0:
    for key in cnt.keys():
        if key%2 and key < n and cnt[key] == 2:
            continue
        else:
            print(0)
            quit()
    print((2**(n//2)) % mod)
else:
    for key in cnt.keys():
        if key % 2 == 0 and key < n and cnt[key] == 2:
            continue
        elif key == 0 and cnt[key] == 1:
            continue
        else:
            print(0)
            quit()
    print((2**(n//2)) % mod)

Solution (Python):
from collections import defaultdict, deque, Counter
from heapq import heappush, heappop, heapify
import math
import bisect
import random
from itertools import permutations, accumulate, combinations, product
import sys
import string
from bisect import bisect_left, bisect_right
from math import factorial, ceil, floor
from operator import mul
from functools import reduce



sys.setrecursionlimit(2147483647)
INF = float('inf')
def LI(): return list(map(int, sys.stdin.readline().split()))
def I(): return int(sys.stdin.readline())
def LS(): return sys.stdin.readline().split()
def S(): return sys.stdin.readline().strip()
def IR(n): return [I() for i in range(n)]
def LIR(n): return [LI() for i in range(n)]
def SR(n): return [S() for i in range(n)]
def LSR(n): return [LS() for i in range(n)]
def SRL(n): return [list(S()) for i in range(n)]
def MSRL(n): return [[int(j) for j in list(S())] for i in range(n)]
mod = 1000000007


n = I()
L = sorted(LI())
l = 0
r = n - 1
A = []
while r >= 0:
    A += [abs(r - l)]
    l += 1
    r -= 1


if sorted(A) != L:
    print(0)
else:
    s  = len(set(L))
    if n % 2:
        s -= 1
    print(pow(2, s, mod))

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

Solution (Python):
def __is_even(num):
    return num % 2 == 0


DIVISOR = 10 ** 9 + 7
ITR_NUM = 1000

N = int(input())
reported_num_count = {}
power_num = 0
if __is_even(N):  
    
    for i in range(1, N, 2):
        reported_num_count[i] = 0
    for i in list(map(int, input().split())):
        if (1 <= i <= N - 1) and not __is_even(i) and reported_num_count[i] < 2:
            reported_num_count[i] += 1
        else:
            print(0)
            exit()
    power_num = int(N / 2)
else:  
    
    for i in range(0, N, 2):
        reported_num_count[i] = 0
    for i in list(map(int, input().split())):
        if (i == 0) and reported_num_count[0] < 1:
            reported_num_count[0] += 1
        elif (2 <= i <= N - 1) and __is_even(i) and reported_num_count[i] < 2:
            reported_num_count[i] += 1
        else:
            print(0)
            exit()
    power_num = int((N - 1) / 2)

result = 1
while power_num > ITR_NUM:
    result *= 2 ** ITR_NUM % DIVISOR
    result %= DIVISOR
    power_num -= ITR_NUM
result *= 2 ** power_num % DIVISOR
print(result % DIVISOR)

Solution (Python):
def main():
    import sys
    input = sys.stdin.readline
    N = int(input())
    A = list(map(int,input().split()))
    mod = 10**9+7
    
    from collections import defaultdict
    D = defaultdict(int)
    for i in A:
        D[i] += 1
    flag = 0
    for i in D:
        if i==0 and D[i] != 1:
            flag = 1
            break
        if i!=0 and D[i] != 2:
            flag = 1
            break
    if flag == 1:
        print(0)
    else:
        print(pow(2,N//2,mod))
    
    
main()

Solution (Python):

import sys
input = sys.stdin.readline
sys.setrecursionlimit(2147483647)
INF=float("inf")
MOD=10**9+7



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

"""
Nが奇数個の場合、
    Aiに奇数の数字があったらNG
    0の数は1つだけ
    2^(N//2)通り

偶数個の場合
    Aiに偶数の数字があったらNG
    0は0個
    2^((N-1)/2)通り→2^(N//2)でOK

同じ数字は2個ある
"""

from collections import Counter
c = Counter(A)

def ng():
    print(0)
    exit()


if N%2 == 1:
    for k, v in c.items():
        if k % 2 == 1:
            ng()

        if k != 0:
            if v != 2:
                ng()

    if c[0] != 1:
            ng()

else:
    for k, v in c.items():
        if k % 2 == 0:
            ng()

        if k != 0:
            if v != 2:
                ng()

    if c[0] != 0:
            ng()

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

Solution (Python):

import collections

N = int(input().split()[0])
a_list = list(map(int, input().split()))

excepted_dict = {}

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

counter = collections.Counter(a_list)

mod = 10 ** 9 + 7

if dict(counter) == expected_dict:
    c = 1
    for v in counter.values():
        c = ((c % mod) * (v % mod)) % mod
    ans = c
else:
    ans = 0

print(ans)

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

if n%2==0:
    evenlists=[]
    for i in range(1,n,2):
        evenlists.append(i)
        evenlists.append(i)
    special=sorted(evenlists)
    
    if special==sorted(lists):
        ans=1
        for i in range(int(n/2)):
            ans=ans*2
            ans=ans%(10**9+7)
        print(ans)
    else:
        print(0)
else:
    oddlists=[]
    for j in range(2,n,2):
        oddlists.append(j)
        oddlists.append(j)
    oddlists.append(0)
    special=sorted(oddlists)
    
    if special==sorted(lists):
        ans=1
        for j in range(int((n-1)/2)):
            ans=ans*2
            ans=ans%(10**9+7)
        print(ans)  
    else:
        print(0)

Solution (Python):

import sys

MOD = 1000000007  

def solve(N: int, A: "List[int]"):
    from collections import Counter
    c = Counter(A)

    for k,v in c.items():
        if(v == 2 or (k == 0 and v == 1)):
            pass
        else:
            print(0)
            exit()
        
    print((2 ** (N//2))%MOD)


    return



def main():
    def iterate_tokens():
        for line in sys.stdin:
            for word in line.split():
                yield word
    tokens = iterate_tokens()
    N = int(next(tokens))  
    A = [ int(next(tokens)) for _ in range(N) ]  
    solve(N, A)

if __name__ == '__main__':
    main()

Solution (Python):
def solve():
    N = int(input())
    A = map(int, input().split())
    count = [0] * N
    ex = [i*2 if N%2!=i%2 else 0 for i in range(N)]
    for a in A:
        count[a] += a
    
    if count == ex:
        return 2**(N//2) % (10**9+7)
    else:
        return 0
    
if __name__ == '__main__':
    print(solve())

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


mod=10**9+7


Asorted = sorted(A,reverse=True)

for i in range(0,len(A)-1,2):

    if Asorted[i]==Asorted[i+1]==N-i-1:
        
        pass
    else:
        print("0")
        exit(0)


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

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

false_flag = 0
'''
if N % 2 == 0:
    count_ = 1
else:
    if A.count(0) != 1:
        false_flag = 1
    count_ = 2
while count_ < N and false_flag == 0:
    if A.count(count_) != 2:
        false_flag = 1
    count_ += 2
'''

count_list = [0 for i in range(N)]
for index in A:
    count_list[index] += 1

if N % 2 == 0:
    count_ = 1
    diff = -1
else:
    if count_list[0] != 1:
        false_flag = 1
    count_ = 2
    diff = -1
while count_ < N and false_flag == 0:
    
    if count_list[count_] != 2 or count_list[count_ + diff] != 0:
        false_flag = 1
    count_ += 2

if false_flag == 0:
    print((2 ** (N // 2) ) % 1000000007)
else:
    print(0)

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

Solution (Python):
from collections import Counter

ans_0 = False
N = int(input())
l = list(map(int, input().split()))
l_Counter = Counter(l)
if N % 2 == 1:
    if l_Counter[0] != 1:
        ans_0 = True
    else:
        l_Counter[0] = 2
        for i in l_Counter.items():
            
            if i[1] != 2 or i[0] % 2 == 1:
                ans_0 = True
                break
else:
    for i in l_Counter.items():
        
        if i[1] != 2 or i[0] == 0 or i[0] % 2 == 0:
            ans_0 = True
            break


if ans_0:
    print(0)
else:
    print((2 ** (N // 2)) % 1000000007)

Solution (Python):
mod = 1000000007

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

data = [0]*N
for i in a:
  data[i] += 1

cnt = 0
for i in range(1,len(data)):
  if data[i] == 2:
    cnt += 1
  elif data[i] == 0:
    continue
  else:
      print(0)
      exit()
print(pow(2, cnt) %mod)

Solution (Python):
n = int(input())
A = [int(num) for num in input().split()]
import collections as cl
dic = cl.Counter(A)

cont = False
if n % 2 == 1:
  if dic[0] != 1:
    cont = True
  else:
    dic[0] = 2
    for num in dic.values():
      if num != 2:
        cont = True
        break
else:
  for num in dic.values():
    if num != 2:
      cont = True
      break

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

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

D = [0] * n

for i in range(n):
    D[A[i]] += 1

ok = 1
if n % 2 == 0:
    for i in range(1, n, 2):
        if D[i] != 2:
            ok = 0
            break
else:
    if D[0] != 1:
        ok = 0
    for i in range(2, n//2+1, 2):
        if D[i] != 2:
            ok = 0
            break

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

print(ans)

Solution (Python):
n = int(input())
b = list(map(int,input().split()))
a = set(b)
flag = 0
if n % 2 == 1:
    if all(i % 2 == 0 for i in a) and len(a) == (n-1)//2 +1 and b.count(0) == 1:
        flag = 1
else:
    if all(i % 2 == 1 for i in a) and len(a) == (n-1)//2 + 1:
        flag = 1
print(2**(n//2)%(10**9+7) if flag==1 else 0)

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

Solution (Python):
N = int(input())
A = [int(i) for i in input().split()]
A.sort()
f = True
mod = 10 ** 9 + 7

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

if f:
  print(2 ** (N//2) % mod)
else:
  print(0)

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

def main():
    N = int(input())
    a = sorted(list(map(int, input().split())), reverse=True)

    MOD = int(1e9) + 7

    tmp = N - 1
    ans = 1
    for i in range(N//2):
        
        if a[2*i] == tmp and a[2*i+1] == tmp:
            
            ans *= 2
            ans %= MOD
        else:
            print(0)
            return
        tmp -= 2
    
    if N&1:
        if a[N-1] != 0:
            print(0)
            return
    
    print(ans)

if __name__ == "__main__":
    main()

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