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):
from collections import Counter
n = int(input())
a = list(map(int, input().split()))
c = Counter(a)
d = list(c.values())
if (n % 2 == 1 and c[0] == 1 and d.count(2) == (n-1)//2) or (n % 2 == 0 and d.count(2) == n//2):
    print(pow(2, n//2, 10**9+7))
else:
    print(0)

Solution (Python):
MOD=1e9+7

from collections import defaultdict
def check_even(c):
	ans=1
	d=defaultdict(int)
	for i in range(len(c)):
		d[c[i]]+=1
	
		if c[i]>=len(c) or c[i]%2==0 or d[c[i]]>2:
			return 0
		
		if d[c[i]]==1:
			ans=ans*2 % MOD
	return int(ans)
		
def check_odd(c):
	ans=1
	d=defaultdict(int)
	for i in range(len(c)):
		d[c[i]]+=1
		if c[i]>=len(c) or c[i]%2==1 or d[0]>1 or d[c[i]]>2:
			return 0
		
		if c[i]!=0 and d[c[i]]==1:
			ans=ans*2%MOD
			
	return int(ans)
		
n=int(input())
c=list(map(int,input().split()))
if n%2==0:
	print(check_even(c))
else:
	print(check_odd(c))

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

if n % 2 == 1:
    ex = [0]
    
    for i in range(n//2):
        a = 2 * (i+1)
        ex += [a,a]
        
else:
    ex = []
    a = 1
    
    for i in range(n//2):
        ex += [a,a]
        a += 2
        
ans = 0

if A == ex:
    ans = 2 ** (n//2) % (10**9 + 7)
    
print(ans)

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
a.sort()
res = True
anse = list(i for i in range(1, n, 2))
anso = list(i for i in range(2, n, 2))
if n % 2 != 0:
  if a[0] != 0:
    res = False
    print(0)
  a = a[1:]
  for i in range(0, len(a), 2):
    if a[i] != anso[i//2] or a[i+1] != anso[i//2]:
        print(0)
        res = False
        break


if n % 2 == 0:
    for i in range(0, len(a), 2):
        if a[i] != anse[i//2] or a[i+1] != anse[i//2]:
            print(0)
            res = False
            break

p = 10**9 + 7
if res:
  print(pow(2, n//2, p))

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

p = 10**9 + 7
if res:
  print(pow(2, n//2, p))

Solution (Python):
import math
from math import gcd,pi,sqrt
INF = float("inf")
MOD = 10**9 + 7

import sys
sys.setrecursionlimit(10**6)
import itertools
import bisect
from collections import Counter,deque
def i_input(): return int(input())
def i_map(): return map(int, input().split())
def i_list(): return list(i_map())
def i_row(N): return [i_input() for _ in range(N)]
def i_row_list(N): return [i_list() for _ in range(N)]
def s_input(): return input()
def s_map(): return input().split()
def s_list(): return list(s_map())
def s_row(N): return [s_input for _ in range(N)]
def s_row_str(N): return [s_list() for _ in range(N)]
def s_row_list(N): return [list(s_input()) for _ in range(N)]


def main():
    n = i_input()
    l = i_list()
    l.sort()

    if n == 1:
        if 0 in l:
            print(1)
            exit()
        else:
            print(0)
            exit()


    L = {}
    for i,k in itertools.groupby(l):
        L[i] = len(list(k))

    cnt = 0

    for i, k in L.items():
        if i == 0:
            if k > 1:
                print(0)
                exit()
        else:
            if k != 2:
                print(0)
                exit()
            else:
                cnt += 1
    print(2**cnt % MOD)









if __name__=="__main__":
    main()

Solution (Python):
n = int(input())
alst = list(map(int, input().split()))
num = n - 1
ans_lst = [abs(i) for i in range(-num, num + 1, 2)]
alst.sort()
ans_lst.sort()
if alst != ans_lst:
    print(0)
else:
    MOD = 10 ** 9 + 7
    ans = pow(2, n // 2, MOD)
    print(ans)

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

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

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
mod = 10 ** 9 + 7
num_map = [0] * ((n + 2 - 1) // 2)
for i in range(n):
    num_map[a[i] // 2] += 1

res = 2 - n % 2
if num_map[0] != 2 - n % 2:
    print(0)
else:
    for i in range(1, (n + 2 - 1) // 2):
        if num_map[i] != 2:
            print(0)
            break
        else:
            res = res * 2 % mod
    else:
        print(res)

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
mod = 10 ** 9 + 7
num_map = [0] * ((n + 2 - 1) // 2)
for i in range(n):
    num_map[a[i] // 2] += 1

res = 1
if n % 2 == 1:
    if num_map[0] != 1:
        print(0)
    else:
        for i in range(1, (n + 2 - 1) // 2):
            if num_map[i] != 2:
                print(0)
                break
            else:
                res = res * 2 % mod
        else:
            print(res)
else:
    for i in range((n + 2 - 1) // 2):
        if num_map[i] != 2:
            print(0)
            break
        else:
            res = res * 2 % mod
    else:
        print(res)

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):
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**(math.floor(N/2))%(10**9+7))
else:
    print(0)

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

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

Solution (Python):
mod = 10**9+7
n =int(input())
A = list(map(int,input().split()))
tmp = []
for i in range(n):
    tmp.append(abs(n-2*i-1))
A.sort()
tmp.sort()
for a,t in zip(A,tmp):
    if a!=t:
        print(0);exit()
from collections import Counter
from math import factorial
ans = 1
cnt_a = Counter(A)
for k,v in cnt_a.items():
    ans *= factorial(v)
    ans %=mod
print(ans)

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//2):
        if a[i*2]!=i*2+1 or a[i*2+1]!=i*2+1:
            print(0)
            exit()
    
    print((2**(n//2))%mod)


else:
    if a[0]!=0:
        print(0)
        exit()
    
    b=a[1:]

    for i in range(n//2):
        if b[i*2]!=i*2+2:
            print(0)
            exit()
        
        if b[i*2+1]!=i*2+2:
            print(0)
            exit()

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

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

def f(x):
 for i in range(x,N,2):
  if A[i-1]!=i or A[i]!=i:
    return 0
 return 1   
    
a=1
if N%2==0:a=f(1)
else: a=A[0]==0 and f(2)
print(2**(N//2)%(10**9+7)*a)

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

def f(x):
 for i in range(x,N,2):
  if A[i-1]!=i or A[i]!=i:
    return 0
 return 1   
    
a=1
if N%2==0:a=f(1)
else:
 if A[0]!=0:a=0
 else:a=f(2)
print(2**(N//2)%(10**9+7)*a)

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

def f(x):
 for i in range(x,N,2):
  if A[i-1]!=i or A[i]!=i:
    return False
 return True   
    
a=True
if N%2==0:a=f(1)
else:
 if A[0]!=0:a=False
 else:a=f(2)
print(2**(N//2)%(10**9+7) if a else 0)

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

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

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

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

Solution (Python):
import math

def fail():
    print(0)
    exit()

def main():
    n = int(input())
    As = list(map(int, input().split(' ')))
    ind_lis = {}
    idx = n - 1
    while idx >= 0:
        ind_lis[idx] = 0
        idx -= 2
    for a in As:
        if a not in ind_lis:
            fail()
        ind_lis[a] += 1
        if a == 0 and ind_lis[a] > 1:
            fail()
        elif ind_lis[a] > 2:
            fail()
    print(2**(n//2)%(10**9 + 7))



if __name__ == '__main__':
    main()

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

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

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

L = A[:]
L = list(set(L))

mod = 10 ** 9 + 7

d = defaultdict(int)
for i in range(N):
    d[A[i]] += 1

if N % 2 == 1:
    bfr = 0
    for i in L:
        if i - bfr != 2 and i != 0:
            print(0)
            exit()

        if i == 0:
            if d[i] != 1:
                print(0)
                exit()
            else:
                continue
        if d[i] != 2:
            print(0)
            exit()
        bfr = i

    print((2 ** (N // 2)) % mod)
else:
    bfr = 1
    for i in L:
        if i - bfr != 2 and i != 1:
            print(0)
            exit()

        if d[i] != 2:
            print(0)
            exit()
        bfr = i

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

Solution (Python):
N = int(input())
a = list(map(int, input().split()))
Sum = 1
mod = 1000000007

a.sort()
data = []
if N % 2 == 0:
    for i in range(int(N / 2)):
        data.append(1 + i * 2)
        data.append(1 + i * 2)
else:
    data.append(0)
    for i in range(1, N // 2 + 1):
        data.append(i * 2)
        data.append(i * 2)

if a == data:
    for i in range(N // 2):
        Sum *= 2
        Sum %= mod
    print(Sum)
else:
    print(0)

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

Solution (Python):
from collections import Counter

n = int(input())
c = Counter(list(map(int, input().split())))

ans = 0
for k, v in c.items():
    if k == 0:
        if n%2==0 and v > 2:
            print(0)
            exit(0)
        elif n%2==1 and v > 1:
            print(0)
            exit(0)
    else:
        ans += 1
        if v > 2:
            print(0)
            exit(0)

print(pow(2, ans, 10**9+7))

Solution (Python):
N=int(input())
MOD=10**9+7
A=[int(x) for x in input().split()]
flag=1
set1=set()
set2=set()
if N%2==1:
    set1.add(0)
    for j in range(2,N+1,2):
        set1.add(j)
        set2.add(j)
    for i in range(N):
        now=A[i]
        if now in set1:
            set1.remove(now)
        elif now in set2:
            set2.remove(now)
        else:
            flag=0
            break
    if len(set1)!=0 or len(set2)!=0:
        flag=0
else:
    for k in range(1,N+1,2):
        set1.add(k)
        set2.add(k)
    for p in range(N):
        now=A[p]
        if now in set1:
            set1.remove(now)
        elif now in set2:
            set2.remove(now)
        else:
            flag=0
            break
    if len(set1)!=0 or len(set2)!=0:
        flag=0
if flag==0:
    print(0)
else:
    ans=1
    div2=N//2
    for q in range(div2):
        ans*=2
        ans%=MOD
    print(ans)

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

def fast_pow(x, n, MOD):
    res = 1
    while n:
        if n & 1:
            res = res * x % MOD
        x = x * x % MOD
        n >>= 1
    return res


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

d = {}
for i in a:
    if n % 2:
        if i > 0 and i % 2:
            print(0)
            exit()
    else:
        if i > 0 and i % 2 == 0:
            print(0)
            exit()

    if not i in d:
        d[i] = 1
    elif d[i] == 1:
        d[i] += 1
    else:
        print(0)
        exit()

if n % 2:
    if d[0] != 1:
        print(0)
        exit()
    print(fast_pow(2, len(d)-1, MOD))
else:
    if 0 in d:
        print(0)
        exit()
    print(fast_pow(2, len(d), MOD))

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


c = Counter(A)
MOD = 10**9 + 7
if N % 2 == 0:
    is_ok = 1
    cnt = 0
    for num in range(1, N, 2):
        cnt += 1
        if c[num] != 2:
            is_ok=0
            break
    if not is_ok:
        print(0)
        exit()
    print(pow(2, cnt, MOD))
else:
    is_ok = 1
    cnt = 0
    if c[0] != 1:
        is_ok = 0
    for num in range(2, N, 2):
        cnt += 1
        if c[num] != 2:
            is_ok = 0
            break
    if not is_ok:
        print(0)
        exit()
    print(pow(2, cnt, MOD))

Solution (Python):
from collections import Counter

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

if all([v == 2 for k, v in cnt_A.items() if k != 0]):
    print(pow(2, n // 2, 10**9 + 7))
else:
    print(0)

Solution (Python):
from collections import Counter

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

if not all([v == 2 for k, v in cnt_A.items() if k != 0]):
    print(0)
else:
    print(pow(2, n // 2, 10**9 + 7))

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

from collections import defaultdict as dd
Dict = dd(lambda:0)
for a in A:
    Dict[a] += 1

if N & 1: Dict[0] += 1
f = (lambda:(lambda x:0 if x&1 else 2) if N&1 else (lambda x:2 if x&1 else 0))()
Possible = {i:f(i) for i in range(N)}
for key,value in Dict.items():
    if value != Possible[key]:
        print(0)
        exit()
else:
    print(2**(N//2)%1000000007)

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

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

Solution (Python):
n = int(input())
a = list(map(int, input().split()))
a.sort()
if n == 1:
    if a[0] == 0:
        print(1)
    else:
        print(0)
    exit()

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

Solution (Python):
from collections import Counter

N = int(input())
abs_diffs = map(int, input().split())

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

if sorted(abs_diffs) == expected:
    print(2 ** dims % (10 ** 9 + 7))

else:
    print(0)

Solution (Python):
n=int(input())
from collections import Counter as co
c=co(map(int,input().split()))
ans=pow(2,n//2,10**9+7)
if n%2 :
    if 0 not in c or c[0]>1:ans=0
    for i in range(1,n):
        if i%2==0 :
            if i not in c or c[i]!=2:ans=0;break
        else:
            if i in c:ans=0;break
else:
    if 0 in c:ans=0
    for  i in range(1,n):
        if i%2:
            if i not in c or c[i]!=2:ans=0;break
        else:
            if i in c:ans=0;break
print(ans)

Solution (Python):
num = int(input())
t = [int(n) for n in input().split()]
t = sorted(t)

valid = True

if num % 2 == 1: 
  check = list(range(0,num+1,2))[1:]
  
  valid1 = t[0] == 0
  valid2 = check == t[2::2] 
  valid3 = check == t[1::2] 
  valid = valid1 and valid2 and valid3
  
  if not valid:
    print(0)
  else:
    ans = 2**((num-1)//2) % (10**9 + 7)
    print(ans)
  
else: 
  check = list(range(1,num,2))
  
  valid1 = True
  valid2 = check == t[::2] 
  valid3 = check == t[1::2] 
  valid = valid1 and valid2 and valid3
  
  if not valid:
    print(0)
  else:
    ans = 2**((num)//2) % (10**9 + 7)
    print(ans)

Solution (Python):
import collections
N = int(input())
A = list(map(int,input().split()))
ans = 1
if 0 in A:
    A.remove(0)
Acounter = collections.Counter(A)
for i in Acounter.values():
    if i == 2:
        continue
    else:
        ans = 0
        break
if ans == 0:
    pass
if ans != 0:
    for i in range(N//2):
        ans = (ans * 2) % (10**9 + 7)
print(ans)

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

else:
    for i in range(1,N,2):
        if i*2 != sum(N_List[i-1:i+1]):
            flg = 1
            break
        else:
            ans = (ans * 2) % ((10**9) +7)

if flg == 0:
    print(ans)
else:
    print(0)

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

cnt = {}
if N & 1:
    bit = 1
else:
    bit = 0

for a in A:
    if a & bit:
        ans = 0
        break
    if a in cnt:
        cnt[a] += 1
    else:
        cnt[a] = 1

for key in cnt.keys():
    if key == 0 and cnt[key] != 1:
        ans = 0
        break
    if key != 0 and cnt[key] != 2:
        ans = 0
        break
else:
    ans = 2**(N//2) %1000000007
print(ans)

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

from collections import Counter
c = Counter(a)

check_ary = []
if n&1:
    check_ary.append(0)

for i in range(n//2):
    for _ in range(2):
        check_ary.append((i+1)*2 if n&1 else i*2+1)

c2 = Counter(check_ary)

if c != c2:
    print(0)
    exit()

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

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


from collections import Counter
c = Counter(a)

def check():
    if n&1:
        if c[0]!=1:
            return False
        for i in range((n-1)//2):
            if c[2*(i+1)] != 2:
                return False
    else:
        for i in range(n//2):
            if c[2*i+1] != 2:
                return False
    return True

if not check():
    print(0)
    exit()

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

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

Solution (Python):
import sys
from collections import defaultdict
def input(): return sys.stdin.readline().strip()
mod = 10**9+7

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

    if N % 2 != 0:
        d = {2 * i: 0 for i in range(N // 2 + 1)}
        for a in A:
            try:
                d[a]  += 1
            except:
                print(0)
                return
        if d[0] != 1:
            print(0)
            return
        for key in d:
            if key == 0: continue
            if d[key] != 2:
                print(0)
                return
    else:
        d = {2 * i + 1: 0 for i in range(N // 2)}
        for a in A:
            try:
                d[a] += 1
            except:
                print(0)
                return
        for key in d:
            if d[key] != 2:
                print(0)
                return
    print(pow(2, N // 2, mod))

if __name__ == "__main__":
    main()

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

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

Solution (Python):
import sys
sys.setrecursionlimit(10 ** 7)
def input() : return sys.stdin.readline().strip()
def INT()   : return int(input())
def MAP()   : return map(int,input().split())
def LIST()  : return list(MAP())
def NIJIGEN(H): return [list(input()) for i in range(H)]
mod=1000000007
N=INT()
L=LIST()
if N%2==0:
  A=range(1,N,2)
  B=range(1,N,2)
else:
  A=range(0,N,2)
  B=range(2,N,2)
A,B=list(A),list(B)
A=A+B
if sorted(A)==sorted(L):
  print(pow(2,N//2,mod))
else:
  print(0)

Solution (Python):
def PowerMod(N,P,Mod):
    if N%Mod==0:
        return 0
    else:
        PowM = 1
        for TP in range(1,P+1):
            PowM = (PowM*N)%Mod
        return PowM

from collections import Counter
N = int(input())
A = sorted(Counter([int(T) for T in input().split()]).most_common(),key=lambda X:X[0])
PassFlag = True
if N%2==1:
    for TA in range(0,(N+1)//2):
        if A[TA][0]!=(2*TA) or A[TA][1]!=(1+(A[TA][0]!=0)):
            PassFlag = False
            break
    print([0,PowerMod(2,(N-1)//2,10**9+7)][PassFlag])
else:
    for TA in range(0,N//2):
        if A[TA][0]!=(2*TA+1) or A[TA][1]!=2:
            PassFlag = False
            break
    print([0,PowerMod(2,N//2,10**9+7)][PassFlag])

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

mod=10**9+7
a.sort()

if n%2==0:
  b=[]
  for i in range(n//2):
    b.append((i*2+1))
    b.append((i*2+1))
  if a==b:
    ans=1
    for _ in range(n//2):
      ans=ans*2
      ans=ans%mod
      
    print(ans)
    
  else:
    print(0)
    
else:
  b=[0]
  for i in range((n-1)//2):
    b.append(((i+1)*2))
    b.append(((i+1)*2))
    
  if a==b:
    ans=1
    for i in range((n-1)//2):
      ans=ans*2
      ans=ans%mod
      
    print(ans)
      
  else:
    print(0)

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


a = sorted(a)

num = 0
judge = 0

if len(a)%2 == 1:
    if a[0] == 0:
        for i in range(1, n, 2):
            if a[i] == i+1 and a[i+1] == i+1:
                num += 1
            else:
                print(0)
                judge = 1
                break
    else:
        print(0)
        judge=1
else:
    for i in range(0, n, 2):
            if a[i] == i+1 and a[i+1] == i+1:
                num += 1
            else:
                print(0)
                judge = 1
                break
        
if judge == 0:
    result = (2**num)%(10**9+7)
    print(result)

Solution (Python):
def main():
  N = int(input())
  A = [int(a) for a in input().split(" ")]
  A.sort()
 
  if N % 2 == 1 and A.count(0) != 1:
    print(0)
    return 0
  elif N % 2 == 0 and A.count(0) > 0:
    print(0)
    return 0
  
  if N % 2 == 1:
    A.pop(0)
  
  cnt = 0
  while len(A) > 0:
    if A[0] != A[1] or (len(A) > 2 and A[0] == A[1] and A[1] == A[2]):
      print(0)
      return 0
    elif A[0] == A[1] == 2 * cnt + (N % 2) + 1:
      cnt += 1
      A.pop(0)
      A.pop(0)
    else:
      print(0)
      return 0
 
  ans = 1
  for p in range(cnt):
    ans = (ans * 2) % 1000000007
  print(ans)

main()

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

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

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

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
flag=0
A=a.sort()
num=[]

if n%2==0:
    for i in range(1,n,2):
        num.append(i)
        num.append(i)

if n%2==1:
    num=[0]
    for i in range(2,n,2):
        num.append(i)
        num.append(i)

if num==a:
    print(2**(n//2)%(10**9+7))

else:
    print("0")

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



nums = {}
exists = True
if N % 2 == 0:
    for A in As:
        if A in nums:
            nums[A] += 1
        else:
            nums[A] = 1
    for key, value in nums.items():
        if key == 0:
            exists = False
        if value != 2:
            exists = False

else:
    for A in As:
        if A in nums:
            nums[A] += 1
        else:
            nums[A] = 1
    for key, value in nums.items():
        if key == 0:
            if value != 1:
                exists = False
        else:
            if value != 2:
                exists = False
if not exists:
    print(0)
else:
    ans = 1
    if N % 2 == 0:
        for i in range(int(N / 2)):
            ans = ans * 2
            ans %= 10**9 + 7
    else:
        for i in range(int((N - 1) / 2)):
            ans = ans * 2
            ans %= 10**9 + 7
            
            
            
    print(ans)

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

from collections import Counter
C=Counter(A)
if n%2==0:
    for i in range(1,n,2):
        if C.get(i) != 2:
            print(0);exit()
else:
    if C.get(0) !=1:
        print(0);exit()
    for i in range(2,n,2):
        if C.get(i)!=2:
            print(0);exit()

n//=2
print(pow(2,n,mod))

Solution (Python):
n = int(input())
a = list(map(int,input().split()))
dic = {}
for i in range(n):
    dic.setdefault(a[i],0)
    dic[a[i]] += 1
ans = 1
for key,value in dic.items():
    
    if n%2==0:
        if n > key and key%2==1 and value==2:
            ans *= 2
        else:
            ans = 0
            break
    
    else:
        if n > key and key%2==0:
            if key==0 and value==1:
                ans *= 1
            elif value==2:
                ans *= 2
            else:
                ans = 0
                break
        else:
            ans = 0
            break
print(ans%(10**9+7))

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

A=tuple(sorted(A))

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

Solution (Python):
from typing import Counter


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

ans = 0
if n % 2 == 0:
    b = Counter(lis)
    flag = 1
    for i in b.values():
        if i == 2:
            pass
        else:
            flag = 0
            break
    if flag:
        ans = 2**(n//2)
        print(ans % mod)
    else:
        print(0)
else:
    lis = sorted(lis)
    lis = lis[1:]
    b = Counter(lis)
    flag = 1
    for i in b.values():
        if i == 2:
            pass
        else:
            flag = 0
            break
    if flag:
        ans = 2**(n//2)
        print(ans % mod)
    else:
        print(0)

Solution (Python):
n = int(input())
a = sorted(list(map(int, input().split())))
if n % 2 == 0:
    b,s = [1,1],3
else:
    b,s = [0],2
for i in range(s,n,2):
    b += [i,i]
if a == b:
    print(pow(2,n//2,1000000007))
else:
    print(0)