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()))
a.sort()
f=1
if n%2==0:
  for i in range(n):
    if i%2==0 and i+1!=a[i] or i%2==1 and i!=a[i]:
      f=0
      break
else:
  for i in range(n):
    if i%2==1 and i+1!=a[i] or i%2==0 and i!=a[i]:
      f=0
      break
if f==0:print(0)
else:
  ans=1
  for j in range(n//2):
    ans*=2
  print(ans%(10**9+7))

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

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

L = [abs((N-1) - 2*i) for i in range(N)]

L.sort(); A.sort()

print(pow(2, (N-N%2)//2, 10**9+7) if L == A else 0)

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

correct = []
if N & 1:
    correct.append(0)
    for i in range(2, N//2 * 2 + 1, 2):
        correct.append(i)
        correct.append(i)
else:
    for i in range(1, N//2 * 2, 2):
        correct.append(i)
        correct.append(i)
print(pow(2, N//2,  int(1e9) + 7) if sorted(A) == correct else 0)

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

correct = []
if N & 1:
    correct.append(0)
    for i in range(2, N//2 * 2 + 1, 2):
        correct.append(i)
        correct.append(i)
else:
    for i in range(1, N//2 * 2, 2):
        correct.append(i)
        correct.append(i)
if sorted(A) == correct:
    print(2 ** (N//2) % (int(1e9) + 7))
else:
    print(0)

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

if n%2!=0:
    if len([0 for c in arr if c==0])!=1 or len(set(arr))!=int(n/2)+1:
    	a=False
else:
    if 0 in arr or len(set(arr))!=int(n/2):
        a=False

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

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

if n%2!=0:
    if len([0 for c in arr if c==0])!=1:
    	a=False
    elif len(set(arr))!=int(n/2)+1:
        a=False
else:
    if 0 in arr:
        a=False
    elif len(set(arr))!=int(n/2):
        a=False

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

Solution (Python):
import math
n=int(input())
arr=list(map(int,input().split()))
ans=True

if n%2!=0:
    if arr.count(0)!=1:
    	ans=False
    elif len(set(arr))!=int(n/2)+1:
        ans=False
else:
    if 0 in arr:
        ans=False
    elif len(set(arr))!=int(n/2):
        ans=False

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

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

def solve(N, A):
    from collections import Counter
    cs = Counter(A)
    if N % 2 == 1:
        if cs[0] != 1:
            return 0
        if any(cs[i] != 2 for i in range(2, N, 2)):
            return 0
    else:
        if any(cs[i] != 2 for i in range(1, N, 2)):
            return 0
    return (2 ** (N // 2)) % 1000000007

print(solve(N, A))

Solution (Python):
N=int(input())
A=[int(i) for i in input().split()]
A.sort()
miss=0

if N%2==0:
    for i in range(int(N/2)):    
        if miss==1:
            break
        for j in range(2):
            if A[0]==2*i+1:
                A.pop(0)
            else:
                miss=1
                break
                
    if miss==1:
        print(0)
    else:
        print(int((2**int(N/2))%(10**9+7)))

else:
    if A[0]!=0:
        miss=1
        A.pop(0)
    else:
        A.pop(0)
    for i in range(int((N-1)/2)):
        if miss==1:
            break
        for j in range(2):
            if A[0]==2*i+2:
                A.pop(0)
            else:
                miss=1
                break
                
    if miss==1:
        print(0)
    else:
        print(int((2**int((N-1)/2))%(10**9+7)))

Solution (Python):
n = int(input())
a = [int(i) for i in input().split()]

a_dict = {}
for v in a:
    if v in a_dict:
        a_dict[v] += 1
    else:
        a_dict[v] = 1

 
if n % 2 == 0:
    possible_list = {i: True for i in range(1, n, 2)}
    for k, v in a_dict.items():
        if v != 2 or k not in possible_list:
            print(0)
            exit()
else:
    possible_list = {i: True for i in range(0, n, 2)}
    if a_dict[0] != 1:
        print(0)
        exit()
    else:
        a_dict[0] = 2
        for k, v in a_dict.items():
            if v != 2 or k not in possible_list:
                print(0)
                exit()
 
print(2 ** (n // 2) % (10 ** 9 + 7))

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

A.sort()
ans = 1
mod = 10**9+7

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

print(ans)

Solution (Python):
N = int(input())
arr = sorted([int(i) for i in input().split()])
ok = True
b = {}
for i in range(N):
    if arr[i] not in b:
        b[arr[i]] = 1
    else:
        b[arr[i]] += 1
if N%2 :
    if b[0] != 1:
        ok = False
    for i in range(1,(N-1)//2+1):
        if ok== False:
            break
        if 2*i not in b or b[2*i]!= 2:
            ok = False
else:
    for i in range(1,N//2+1):
        if 2*i-1 not in b or b[2*i-1] != 2:
            ok = False
            break

if ok :
    print(2**(N//2)%(10**9+7))
else:
    print(0)

Solution (Python):
import sys

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

V=sorted(A)

if N%2==0:
    for i in range(N):
        if V[i]!=i//2*2+1:
            print(0)
            sys.exit()

else:
    for i in range(N):
        if V[i]!=(i+1)//2*2:
            print(0)
            sys.exit()    

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

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

if n%2 == 0:
    for i in range(n):
        if i%2 == 0:
            if not A[i] == i+1:
                print(0)
                break
        else:
            if not A[i] == i:
                print(0)
                break
    else:
        print(2**(n//2)%(10**9+7))
else:
    if not A[0] == 0:
        print(0)
    else:    
        for i in range(1,n):
            if i%2 == 0:
                if not A[i] == i:
                    print(0)
                    break
            else:
                if not A[i] == i+1:
                    print(0)
                    break
        else:
            print(2**((n-1)//2)%(10**9+7))

Solution (Python):
n = int(input())
a_list = list(map(int, input().split()))
zero = a_list.count(0)
D = 1000000000 + 7
a_set = set(a_list)
if zero == 1 and n - 1 == 2 * (len(a_set)-1):
    print(2 ** ((n-1)//2) % D)
elif zero == 0 and n == 2 * len(a_set):
    print(2 ** (n//2) % D)
else:
    print(0)

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

Solution (Python):
def main():
    n = int(input())
    if n % 2 == 0:
        bb = [1, 1]
    else:
        bb = [0]
    while len(bb) < n:
        b = bb[-1] + 2
        bb += [b, b]
    aa = sorted(map(int, input().split()))
    if aa != bb:
        print(0)
    else:
        print(2 ** (n // 2) % 1000000007)


if __name__ == '__main__':
    main()

Solution (Python):
import sys

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

if N == 1:
    if A[0] == 0:
        print(1)
        sys.exit()
    else:
        print(0)
        sys.exit()
        
if N % 2 != 0:
    if A[0] == 0:
        a = A[1:]
        j = 1
        k = 0
        for i in range(0, N//2 + 1, 2):
            if a[k] == a[k+1] == 2*j:
                j += 1
                k += 2
            else:
                print(0)
                sys.exit()
        print((2**(N//2)) % (10**9+7))
        
    else:
        print(0)
else:
    j = 1
    k = 0
    for i in range(0, N//2 + 1, 2):
        if A[k] == A[k+1] == 2*j -1:
            j += 1
            k += 2
        else:
            print(0)
            sys.exit()
    print((2**(N//2)) % (10**9+7))

Solution (Python):
n = int(input())
a = input().split()
a = [int(m) for m in a]
pn = [0]*n
for i in range(n):
    pn[(-a[i] + n - 1)//2] += 1
    if (-a[i] + n - 1)//2 != (a[i] + n - 1)//2:
        pn[(a[i] + n - 1)//2] += 1
for i in range(n):
    if pn[i] > 2:
        print(0)
        exit()
    if n % 2 != 0:
        if pn[(n - 1) // 2] > 1:
            print(0)
            exit()

ans = 1
mod = 10**9 + 7
for i in range(n):
    if i <= (n - 1) // 2:
        ans = (ans * pn[i]) % mod
    else:
        break
print(ans)

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

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

else:
    for i in range(1, n//2+1):
        if a[2*i-2] == a[2*i-1] and a[2*i-2] == 2*i-1:
            continue
        else:
            print(0)
            exit()

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

Solution (Python):
def pow2(x):
    if x == 0:
        return 1
    elif x % 2 == 0:
        return (pow2(x/2) ** 2) % (10**9 + 7)
    else:
        return 2 * pow2(x-1)

N = int(input())
a_arr = list(map(int, input().split()))
flag = 0

count_arr = []
for _ in range((N+1)//2):
    count_arr.append(0)

if N%2 == 0: 
    for a in a_arr:
        if a%2 == 0:
            flag = 1
            break
        else:
            count_arr[(a-1)//2] += 1
            if count_arr[(a-1)//2] > 2:
                break
else:
    for a in a_arr: 
        if a%2 == 1:
            flag = 1
            break
        elif a == 0:
            if count_arr[0] > 0:
                flag = 1
                break
            else:
                count_arr[0] += 1
        else:
            if count_arr[a//2] > 1:
                flag = 1
                break
            else:
                count_arr[a//2] += 1
if flag == 1:
    print(0)
else:
    print(pow2(N//2))

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

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

Solution (Python):
def c_lining_up(N, A):
    
    
    

    
    b = ([] if N % 2 == 0 else [0]) + [k for k in range(1 if N % 2 == 0 else 2, N, 2) for _ in range(2)]

    ans = 2**(N // 2) % (10**9 + 7) if sorted(A) == b else 0
    return ans

N = int(input())
A = [int(i) for i in input().split()]
print(c_lining_up(N, A))

Solution (Python):

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

A.sort()

ans = 0
for i, Ai in enumerate(A):
    
    if i == 0:
        if Ai == 0: mode = 0
        elif Ai == 1: mode = 1
        else: break
        continue
    
    if mode == 0 and Ai != ((i + 1) // 2) * 2: break
    elif mode == 1 and Ai != 1 + (i // 2) * 2: break
    else: continue
else:
    ans = (2 ** (N // 2)) % (10 ** 9 + 7)

print(ans)

Solution (Python):
import sys
import collections
import itertools
import math
import re
from collections import deque

MOD = 10 ** 9 + 7

N = int(input())
A = [int(x) for x in input().split()]
A.sort()

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

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

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

Solution (Python):
N=int(input())
a=list(map(int,input().split()))
b=[0,]*N
err=0
cnt=0
ans=1
for i in range(N):
    b[a[i]]+=1
if N%2 == 0:
    for i in range(1,N,2):
        if b[i]!=2:
            err=1
        cnt+=1
    for i in range(0,N,2):
        if b[i]!=0:
            err=1
else:
    if b[0]!=1:
        err=1
    for i in range(2,N,2):
        if b[i]!=2:
            err=1
        cnt+=1
    for i in range(1,N,2):
        if b[i]!=0:
            err=1
if err == 1:
    print("0")
else:
    for i in range(cnt):
        ans=(ans*2)%(10**9+7)
    print(str(ans))

Solution (Python):
N = int(input())
A = [int(_) for _ in input().split()]
mod = 10**9+7
is_odd = N % 2
table = [0]*N
for a in A:
    table[a] += 1
for i in range(N):
    if is_odd and i == 0 and table[i] == 1:
        continue
    if is_odd and i % 2 == 0 and table[i] == 2:
        continue
    if is_odd and i % 2 == 1 and table[i] == 0:
        continue
    if not is_odd and i % 2 == 0 and table[i] == 0:
        continue
    if not is_odd and i % 2 == 1 and table[i] == 2:
        continue
    print(0)
    exit()
print(2**(N//2) % mod)

Solution (Python):
n = int(input())
a = [int(i) for i in input().split()]



valid = [i + (i+n+1) % 2 for i in range(n)]
a = sorted(a)
if a != valid:
    print(0)
else:
    
    
    
    out = 1
    for i in range(int(n/2)):
        out *= 2
        out %= 10**9+7
    print(out)

Solution (Python):
import collections

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

cou = collections.Counter(A)

if N % 2 == 0:
    for i in cou.keys():
        if i % 2 == 0 or cou[i] % 2 != 0:
            print(0)
            break
    else:
        print((2**(N//2)) % (10**9+7))

else:
    for i in cou.keys():
        if i % 2 != 0 or cou[i] % 2 != 0:
            if i == 0 and cou[i] == 1:
                aa = 1
            else:
                print(0)
                break
    else:
        print((2**((N-1)//2)) % (10**9+7))

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

if n % 2 == 0:
  if len(set(nums)) == n // 2:
    print(2**(n//2) % mod)
  else:
    print(0)
else:
  if len(set(nums))== n // 2 + 1 and nums.count(0) == 1:
    print(2**(n//2) % mod)
  else:
    print(0)

Solution (Python):
n=int(input())
l=list(map(int,input().split()))
nOdd=len(l)%2==1
if nOdd:
    num=[x for x in range(n) if n%2==0]
else:
    num=[x for x in range(n) if n%2!=0]
dic={}
for i in num:
    dic[i]=0
for i in l:
    dic.setdefault(i,0)
    dic[i]+=1
for i,c in dic.items():
    if i==0 and nOdd:
        if c!=1:
            print(0)
            exit()
    elif i==0 and not(nOdd):
        print(0)
        exit()
    elif c!=2:
        print(0)
        exit()
    


print(pow(2,n//2) % 1000000007)

Solution (Python):
n=int(input())
l=list(map(int,input().split()))
nOdd=len(l)%2==1
if nOdd:
    num=[x for x in range(len(l)) if n%2==0]
else:
    num=[x for x in range(len(l)) if n%2!=0]
dic={}
for i in num:
    dic[i]=0
for i in l:
    dic.setdefault(i,0)
    dic[i]+=1
for i,c in dic.items():
    if i==0 and nOdd:
        if c!=1:
            print(0)
            exit()

    elif c!=2:
        print(0)
        exit()
    

        
       

print(pow(2, len(l)//2) % 1000000007)

Solution (Python):
n=int(input())
l=list(map(int,input().split()))
nOdd=len(l)%2==1
if nOdd:
    num=[x for x in range(len(l)) if n%2==0]
else:
    num=[x for x in range(len(l)) if n%2!=0]
dic={}
for i in num:
    dic[i]=0
for i in l:
    dic.setdefault(i,0)
    dic[i]+=1
for i,c in dic.items():
    if i==0 and nOdd:
        if c!=1:
            print(0)
            exit()
    elif i==0 and not(nOdd):
        print(0)
        exit()
    elif c!=2:
        print(0)
        exit()
    

        
       

print(pow(2, len(l)//2) % 1000000007)

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

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

len_A = len(A)
isOdd = len_A % 2 == 1
m = {}

nums = []
if isOdd:
    nums = [i for i in range(len_A) if i % 2 == 0]
    nums.append(0)
else:
    nums = [i for i in range(len_A) if i % 2 != 0]

for n in nums:
    m[n] = 0

for a in A:
    m.setdefault(a, 0)
    m[a] += 1


for k, v in m.items():
    if k == 0:
        if isOdd:
            if v != 1:
                print(0)
                exit()
            else:
                continue
        else:
            print(0)
            exit()
    elif v == 0 or v > 2:
        print(0)
        exit()

print(pow(2, len_A//2) % 1000000007)

Solution (Python):
N = int(input())
L = list(map(int,input().split()))
M = sorted(L,reverse=True)
flag = 1
for i in range(N) :
    if i % 2 == 0 :
        l = M[i]
        if l != (N-i-1) :
            flag = 0
            break
    else :
        if M[i] != l :
            flag = 0
            break
if flag == 0 :
    ans = 0
else :
    ans = (2**(N//2)) % (10**9+7)
print(ans)

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

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

if sorted(a)!=sorted(arr):
    print(0)
    exit()

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

Solution (Python):
N=int(input())
if N%2==0:
    L=[]
    for i in range(int(N/2)):
        L.append(i*2+1)
        L.append(i*2+1)
        
else:
    L=[0]
    for i in range(1,int((N-1)/2)+1):
        L.append(i*2)
        L.append(i*2)

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

if A==L:
    if N%2==0:
        ans=1
        for j in range(int(N/2)):
            ans*=2
            ans%=(10**9+7)
        print(ans)
    else:
        ans=1
        for j in range(int((N-1)/2)):
            ans*=2
            ans%=(10**9+7)
        print(ans)
else:
    print(0)

Solution (Python):
from collections import Counter
N = int( input())
A = Counter(list( map( int, input().split())))
Q = 10**9 + 7
ans = 1
for i in range(N-1, 0, -2):
    if A[i] == 1:
        ans = 0
        break
if N%2 == 1:
    if A[0] != 1:
        ans = 0
print(ans*pow(2,N//2,Q))

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

Solution (Python):
import collections

n=int(input())
l=list(map(int,input().split()))
s=collections.Counter(l)
s=s.most_common()

a=1
if n%2==0:
    for i in s:
        if i[1]!=2:
            print(0)
            exit()
        elif i[0]%2!=1 or i[1]//2>n//2:
            print(0)
            exit()
    else:
        for j in range(n//2):
            a=(2*a)%1000000007
    print(a)
elif n%2==1:
    if (0,1) not in s:
        print(0)
        exit()
    else:
        del s[-1]
        
        for i in s:
            if i[1]!=2 or i[0]%2!=0 or i[0]//2>n//2:
                print(0)
                exit()
        else:
            for j in range(n//2):
                a=(2*a)%1000000007
    print(a)

Solution (Python):
from collections import Counter

M = 10 ** 9 + 7

def main():
    n = int(input())
    a = [int(s) for s in input().split()]
    print(solve(a, n))

def solve(a, n):
    counter = Counter(a)

    if n % 2 == 0:
        for i in range(1, n, 2):
            if counter.get(i, None) != 2:
                return 0
    else:
        if counter.get(0, None) != 1:
            return 0
        for i in range(2, n, 2):
            if counter.get(i, None) != 2:
                return 0

    return modpow(2, n // 2, M)

def modpow(a, b, m):
    r = 1

    while b != 0:
        if b & 0x01:
            r = (r * a) % m
        a = (a * a) % m
        b >>= 1

    return r

main()

Solution (Python):

N = int(input())
An = list(map(int, input().split()))
DIV = 10**9 + 7

import math
def combinations_count(n, r):
    return math.factorial(n) // (math.factorial(n - r) * math.factorial(r))

def permutations_count(n, r):
    return math.factorial(n) // math.factorial(n - r)

abs_cnt = {}
for Ai in An:
    if Ai in abs_cnt:
        abs_cnt[Ai] += 1
    else:
        abs_cnt[Ai] = 1



jijo = 0
if N%2 == 0:
    for k,v in abs_cnt.items():
        if k % 2 == 1 and v == 2:
            jijo += 1
        else:
            print(0)
            exit()
else:
    for k, v in abs_cnt.items():
        if k % 2 == 0 and v == 2:
            jijo += 1
        elif k == 0 and v == 1:
            pass
        else:
            print(0)
            exit()

print(2**jijo%DIV)

Solution (Python):
from collections import Counter


def solve(N, As):
    c = Counter(As)
    n = 10 ** 9 + 7
    if c['0'] == N % 2 and \
            all([v == 2 and int(i) % 2 == (N + 1) % 2 for i, v in c.items() if i != '0']):
        return pow(2, N // 2, n)

    return 0


if __name__ == "__main__":
    N = int(input())
    As = input().split(" ")
    print(solve(N, As))

Solution (Python):
n = int(input())
nums = {0:0}

for i in list(map(int, input().split())):
    if i in nums:
        nums[i] += 1
        if nums[i] > 2:
            ans = 0
            break
    else:
        nums[i] = 1
        
if n % 2 == 0:
    if 1 in nums.values():
        ans = 0
    else:
        ans = 2**(n//2)
        
else:
    if nums[0] == 1:
        del nums[0]
        if 1 in nums.values():
            ans = 0
        else:
            ans = 2**((n-1)//2)
    else:
        ans = 0
        
print(ans % (10**9+7))

Solution (Python):
iN = int(input())
aA = [int(_) for _ in input().split()]
aA.sort()
iD = 10**9 + 7



iRet = 0
if iN % 2 == 0:
    aR = [x if x % 2 == 1 else x + 1 for x in range(iN)]
else:
    aR = [x if x % 2 == 0 else x + 1 for x in range(iN)]
if aA == aR:
    print(pow(2,iN//2,iD))
else:
    print(0)

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

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

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

ans = 1
count = 0
if N == 1:
    if A[0] == 1:
        ans = 1
    else:
        ans = 0

elif N % 2 == 0:
    for i in range(1, int(N/2)+1):
        if A[i*2-1] == 2:
            count += 1
        else:
            ans = 0
else:
    if A[0] == 1:
        for i in range(1, int(N/2)+1):
            if A[i*2] == 2:
                count += 1

            else:
                ans = 0
    else:
        ans = 0
for i in range(count):
    ans *= 2
    ans %= 1000000007
print(ans)

Solution (Python):
def mod_pow(a,p,mod):

    if p == 0:
        return 1
    elif p%2 == 1:
        return a * mod_pow(a,p-1,mod)
    else:
        half = mod_pow(a,p//2,mod) %mod
    return half * half % mod

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

B = [0 for i in range(N)]
max_b = 0
mod =10**9 + 7

for i in range(N):
    B[A[i]] += 1

if N%2 == 1:
    for i,b in enumerate(B):
        if i == 0:
            if b != 1:
                print(0)
                exit()

        elif b != 2 and b != 0:
            print(0)
            exit()
    p = (N - 1)//2

else:
    for i,b in enumerate(B):
        if b != 2 and b != 0:
            print(0)
            exit()
    p = (N)//2

ans = mod_pow(2,p,mod)
print(ans)

Solution (Python):
N=int(input())
s=sorted([i for i in range((N+1)%2, N, 2)]*2)
if N%2 == 1:
    s.pop(0)
print((2**(N//2))%1000000007 if sorted([int(i) for i in input().split()])==s else 0)

Solution (Python):
import sys
N = int(input())
A = list(map(int, input().split()))
A.sort()
MOD = int(1e9) + 7


if N % 2 == 0:
    ans = 1
    for i in range(N//2):
        if A[2*i] == A[2*i+1] == 2*i+1:
            ans *= 2
            ans %= MOD
        else:
            print(0)
            sys.exit()
            
else:
    if A[0] == 0:
        ans = 1
    else:
        print(0)
        sys.exit()

    for i in range(N//2):
        if A[2*i+1] == A[2*i+2] == 2*(i+1):
            ans *= 2
            ans %= MOD
        else:
            print(0)
            sys.exit()
print(ans)

Solution (Python):
N = int(input())
mod = int(1e9+7)
A = sorted(list(map(int, input().split())))


N_mod = N%2
if N == 1:
    if A[0] == 0:
        print(1)
        exit()
    else:
        print(0)
        exit()
    
if N_mod == 1 and A[0] == 0:
    A = A[1:]
    num = 2
else:
    num = 1
ans = 1
for i in range(0, N-N_mod, 2):
    if A[i] == A[i+1] and A[i] == num:
        ans = int(ans * 2)
        ans = int(ans % mod)
        num += 2
    else:
        ans = 0
        break
print(ans)

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

s=list(sorted(s))
if n%2==1:
    s.remove(0)
    for i in range(n-1):
        s[i] -= 1

a = []
for i in range(n//2):
    a.append(2*i+1)

if s[0::2]==s[1::2] and s[0::2] ==a :
    print((2**((len(s))//2))%(10**9+7))
else:
    print(0)

Solution (Python):
N = int(input())
A = [int(_) for _ in input().split()]
A.sort()
mod = 7 + 10**9
Appropriate = True
ans = 1

if N % 2 == 0: 
    i = 0
    while i < N:
        if A[i] != i+1 or A[i+1] != i+1:
            Appropriate = False
            break
        else:
            ans *= 2
            ans %= mod
            i+=2
else: 
    i = 1
    if A[0] != 0 or A.count(0) > 2:
        Appropriate = False
    else:
        while i < N:
            if A[i] != i+1 or A[i+1] != i+1:
                Appropriate = False
                break
            else:
                ans *= 2
                ans %= mod
                i += 2

print(ans if Appropriate else 0)

Solution (Python):



n = int(input())
a = [int(i) for i in input().split()]
mod = 10 ** 9 + 7
b = [0] * n

for ai in a:
    if n % 2 == ai % 2:
        break
    left = (n - ai) // 2
    right = (n + ai) // 2
    if b[left] == 0:
        b[left] = 1
    elif b[right] == 0:
        b[right] = 1
    else:
        break

if 0 in b:
    ans = 0
elif n % 2 == 0:
    ans = pow(2, len(set(a)), mod)
else:
    ans = pow(2, len(set(a)) - 1, mod)
print(ans)

Solution (Python):
from collections import defaultdict, Counter
from itertools import product, groupby, count, permutations, combinations
from math import pi, sqrt
from collections import deque
from bisect import bisect, bisect_left, bisect_right
from string import ascii_lowercase
from functools import lru_cache
import sys
sys.setrecursionlimit(10000)
INF = float("inf")
YES, Yes, yes, NO, No, no = "YES", "Yes", "yes", "NO", "No", "no"
dy4, dx4 = [0, 1, 0, -1], [1, 0, -1, 0]
dy8, dx8 = [0, -1, 0, 1, 1, -1, -1, 1], [1, 0, -1, 0, 1, 1, -1, -1]


def inside(y, x, H, W):
    return 0 <= y < H and 0 <= x < W


def ceil(a, b):
    return (a + b - 1) // b


def main():
    N = int(input())
    C = Counter(list(map(int, input().split())))
    MOD = 10 ** 9 + 7

    ans = 1
    num_zero = 0
    for k, v in C.items():
        if k == 0:
            num_zero += 1
        elif v == 2:
            ans *= 2
            ans %= MOD
        else:
            print(0)
            return
    
    if N % 2 != num_zero:
        print(0)
        return

    print(ans)


if __name__ == '__main__':
    main()

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

Solution (Python):
il = lambda: list(map(int, input().split()))
ils = lambda n, s="int(input())": [eval(s) for _ in range(n)]
mod = int(1e9+7)

n = int(input())
a = il()
dic = dict()
for i in a:
    if i in dic:
        dic[i] += 1
    else:
        dic[i] = 1
flag = 1
for i, j in dic.items():
    if i == 0:
        if j != 1:
            flag = 0
    else:
        if j != 2:
            flag = 0
if flag:
    print(pow(2, n//2)%mod)
else:
    print(0)

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

A.sort()

i = 0

if N%2 == 1:
  if A[0] != 0:
    print(0)
    exit(0)
  i = 1

cnt = 0

while i < N:
  if i+1 == A[i] and i+1 == A[i+1]:
    cnt += 1
    i = i + 2
    continue
  else:
    print(0)
    exit(0)
    
ans = 1
for j in range(cnt):
  ans = ans * 2 % int(1e9 +7)
  
print(ans)

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

def f():
    As = sorted(A)
    if N % 2:
        if As[0] != 0: return 0
        if any((i // 2 + 1)*2 != a for i,a in enumerate(As[1:])): return 0
    else:
        if any((i // 2)*2 + 1 != a for i,a in enumerate(As)): return 0
    return pow(2, N//2, 10**9 + 7)

print(f())

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

from collections import Counter
def f():
    cnt = Counter(A)
    m = N - 1
    for k, v in cnt.items():
        if k == 0:
            if v == 1:
                continue
            else:
                return 0
        else:
            if v != 2 or k > m:
                return 0
    return pow(2, N//2, 10**9 + 7)

print(f())

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

from collections import Counter

def f():
    cnt = Counter(A)
    m = N - 1
    for k, v in cnt.items():
        if k == 0 and v == 1: continue
        if v != 2 or k > m:
            return 0
    return pow(2, N//2, 10**9 + 7)

print(f())