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 defaultdict

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

mod = 10 ** 9 + 7
c = defaultdict(int)
for a in A:
    if a != 0:
        x = (N - 1 + a) // 2
        y = (N - 1 - a) // 2
        c[(x, y)] += 1

ans = 1
for v in c.values():
    if v == 2:
        ans *= 2
    else:
        ans = 0
        break
    ans %= mod
print(ans)

Solution (Python):
from collections import defaultdict
N = int(input())
A = [int(x) for x in input().split()]
p = 10 ** 9 + 7
C = defaultdict(int)
mod = 1 - N % 2
for a in A:
  if a % 2 != mod:
    print(0)
    break
  elif a >= N:
    print(0)
    break
  else:
    C[a] += 1
    if a and C[a] > 2:
      print(0)
      break
    elif a == 0 and C[a] > 1:
      print(0)
      break
else:
  print(2 ** (N // 2) % p)

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
A.sort()
def main():
    if A[0] == N % 2:
        print(0)
        return 0
    if len(A) == 1 and A[0] == 0:
        print(1)
        return 0
    elif len(A) == 1:
        print(0)
        return 0
    if A[0] == 0:
        del A[0]
    if A[0] == 0:
        print(0)
        return 0
    i = 1
    while True:
        if i >= len(A):
            break
        if len(A) % 2 != 0:
            print(0)
            return 0
        if A[i] != A[i - 1]:
            print(0)
            return 0
        i += 2
    i = 2
    while True:
        if i >= len(A):
            break
        if A[i] == A[i - 1]:
            print(0)
            return 0
        i += 2
    print(pow(2, len(A) // 2) % 1000000007)
main()

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

dic = {}
ans = 1

for Ai in A:
    if Ai not in dic:
        dic[Ai] = 1
    else:
        dic[Ai] += 1

for t in dic.items():
    ans *= N % 2 != t[0] % 2

    if t[0] == 0:
        ans *= t[1] == 1
    else:
        ans = (ans * 2 * (t[1] == 2)) % (10 ** 9 + 7)

print(ans)

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

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

Solution (Python):
n=int(input())
a=list(map(int, input().split()))
import math
x=[0 for _ in range(n)]
if n%2!=0:
    x[0]+=1
for i in range(n):
    x[a[i]]+=1

j=True
for t in x:
    if t%2!=0:
        j=False
print(2**(n//2)%(10**9+7) if j else 0)

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

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

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

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

if N%2:
    for i in range(2,N,2):
        if ctr[i] != 2:
            print(0)
            exit()
else:
    for i in range(1,N,2):
        if ctr[i] != 2:
            print(0)
            exit()

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

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

    
    if N % 2 == 0:
        B = [i for i in range(1, N, 2) for _ in range(2)]
    else:
        B = [0] + [i for i in range(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())
input_list = sorted([int(i) for i in input().split()])

mod = 10 ** 9 + 7

if N % 2 == 1:
    if input_list[0] != 0:
        print(0)
    else:
        if N == 1:
            print(1)
        flag = 2
        limit = (N - 1) // 2
        for i in range(1, limit, 2):
            if input_list[i] == flag and input_list[i+1] == flag:
                flag += 2
                if i == limit-1:
                    print((2**limit) % mod)
            else:
                print(0)
                break
elif N % 2 == 0:
    flag = 1
    limit = N
    for i in range(0, limit, 2):
        if input_list[i] == flag and input_list[i+1] == flag:
            flag += 2
            if i == limit-2:
                print((2**(N//2)) % mod)
                break
        else:
            print(0)
            break

Solution (Python):
N=int(input())
A=list(map(int,input().split()))
B=[0]*(N//2+N%2)
IndexCount=0
IndexRe=0
Divider=pow(10,9)+7
ans=1
if N%2==0:
    for i in range(N):
        if A[i]%2==1 and (A[i]+1)/2<=N/2:
            B[(A[i]-1)//2]+=1
        else:
            print(0)
            exit()
    for i in range((N//2+N%2)):
        if B[i]!=2:
            print(0)
            exit()
    IndexCount=int((N/2)//1000)
    IndexRe=int((N/2)%1000)
    for i in range(IndexCount):
        ans=(ans*(pow(2,1000)%Divider))%Divider
    ans=(ans*(pow(2,IndexRe)%Divider))%Divider
    print(ans)
elif N%2==1:
    for i in range(N):
        if A[i]%2==0 and A[i]/2<=(N-1)/2:
            B[A[i]//2]+=1
        else:
            print(0)
            exit()
    if B[0]!=1:
        print(0)
        exit()
    for i in range((N//2+N%2)-1):
        if B[i+1]!=2:
            print(0)
            exit()
    IndexCount=int(((N-1)/2)//1000)
    IndexRe=int(((N-1)/2)%1000)
    for i in range(IndexCount):
        ans=(ans*(pow(2,1000)%Divider))%Divider
    ans=(ans*(pow(2,IndexRe)%Divider))%Divider
    print(ans)
else:
    print(0)

Solution (Python):

"""
Created on Thu Aug 23 22:15:42 2018
ABC050C
@author: maezawa
"""

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

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

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

    flag = True
    for i in range(n):
        if rec[i] > 2:
            flag = False

    if rec[0] == 0 and flag:
        print((2 ** (n // 2)) % mod)
    else:
        print(0)
else:
    for i in range(n):
       rec[a[i]] += 1

    flag = True
    for i in range(n):
        if rec[i] > 2:
            flag = False

    if rec[0] == 1 and flag:
        print((2 ** (n // 2)) % mod)
    else:
        print(0)

Solution (Python):
import itertools
n = int(input())
a = list(map(int,input().split()))
g = itertools.groupby(sorted(a))
for i,(k,v) in enumerate(g):
    if n%2==1:
        f1 = i==0 and k==0 and len(list(v))==1
        f2 = i!=0 and k==i*2 and len(list(v))==2
        if not (f1 or f2):
            print(0)
            exit()
    else:
        if k!=2*i+1 or len(list(v))!=2:
            print(0)
            exit()
print((2**(n//2))%(10**9+7))

Solution (Python):

from collections import Counter

def main():
    n = int(input())
    a_list = list(map(int, input().split()))
    counter = Counter(a_list)
    ans = 1

    if n % 2 == 0:
        if all(counter[i] == 2 for i in range(1, n, 2)):
            ans = 2 ** (n // 2)
        else:
            ans = 0
    else:
        if all(counter[i] == 2 for i in range(2, n, 2)) and counter[0] == 1:
            ans = 2 ** (n // 2)
        else:
            ans = 0
    print(ans % (10 ** 9 + 7))
        
if __name__ == '__main__':
    main()

Solution (Python):

from collections import Counter

def main():
    n = int(input())
    a_list = list(map(int, input().split()))
    counter = Counter(a_list)

    ans = 1
    if n % 2 != 0:
        for i in range(0, n, 2):
            c = counter[i]
            if (i == 0 and c != 1) or c == 0:
                print(0)
                exit()
            else:
                ans *= c
    else:
        for i in range(1, n, 2):
            c = counter[i]
            if c == 0:
                print(0)
                exit()
            else:
                ans *= c
    print(ans % (10 ** 9 + 7))
        
if __name__ == '__main__':
    main()

Solution (Python):
from collections import Counter

n = int(input())
a = tuple(map(int, input().split(" ")))



a_counter = Counter(a)
a_counter[int(n%2==0)] = 2

if set(a_counter.values()) == {2}:
    print((2 ** (n//2)) % (10**9+7))
else:
    print(0)

Solution (Python):

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

cnt = [0 for i in range(N)]
ans = 1

if N % 2 == 0:
    for i in range(N):
        if A[i] % 2 == 0:
            print(0)
            exit()
        cnt[A[i]] += 1
        if cnt[A[i]] > 2:
            print(0)
            exit()
        if cnt[A[i]] == 1:
            ans = (ans * 2) % (10 ** 9 + 7)
    print(ans)
else:
    for i in range(N):
        if A[i] % 2 == 1:
            print(0)
            exit()
        if A[i] > 0:
            cnt[A[i]] += 1
            if cnt[A[i]] > 2:
                print(0)
                exit()
            if cnt[A[i]] == 1:
                ans = (ans * 2) % (10 ** 9 + 7)
        if A[i] == 0:
            cnt[0] += 1
            if cnt[0] > 1:
                print(0)
                exit()
    print(ans)

Solution (Python):
from collections import Counter
N = int(input())
A = Counter(map(int, input().split()))
f = True
if N == 1 and A[0] == 1:
    print(1)
    exit()

if N % 2 == 1:
    if A[0] != 1:
        f = False
    else:
        del A[0]
    if set(A) != set(range(2, N, 2)) or set(A.values()) != {2}:
        f = False
else:
    if set(A) != set(range(1, N, 2)) or set(A.values()) != {2}:
        f = False
if not f:
    print(0)
else:
    print(2 ** len(A) % (10 ** 9 + 7))

Solution (Python):
from collections import Counter

MOD = 10**9+7

def judge(N: int, A: list) -> int:
    
    cnt = Counter(A)
    
    
    if N%2 == 1:
        
        for k,v in cnt.items():
            if k==0:
                if v != 1:
                    return 0
            else:
                if v != 2:
                    return 0
        
        
        ans = 1
        for i in range(N//2):
            ans = (ans*2) %MOD
        
        return ans
    
    else:
        
        for k,v in cnt.items():
            if v != 2:
                return 0
            
        
        ans = 1
        for i in range(N//2):
            ans = (ans*2) %MOD
        
        return ans
                
N = int(input())
A = list(map(int, input().split()))

print(judge(N,A))

Solution (Python):
from collections import Counter
n=int(input())
l=Counter(map(int,input().split()))
o=int(1e9+7)
if n%2:
  if not (0 in l and l[0]==1):
    print(0)
  elif n//2!=list(l.values()).count(2):
    print(0)
  else:
    print(2**(n//2)%o)
else:
  if n//2!=list(l.values()).count(2):
    print(0)
  else:
    print(2**(n//2)%o)

Solution (Python):
import collections
N = int(input())
a = list(map(int,input().split()))
mod = (10**9+7)
if N%2 !=0:
    if sum(a)%2!=0 or max(a)>N or a.count(0)!=1 or len(set(a))!=N//2+1:
        print(0)
    else:
        print(2**(len(set(a))-1)%mod)
elif N%2 ==0:
    if sum(a)%2!=0 or max(a)>N or len(set(a))!=N//2:
        print(0)
    else:
        print(2**len(set(a))%mod)

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

exp = []
if n % 2 == 0:
    for i in range(0, n // 2):
        exp.append(2 * i + 1)
        exp.append(2 * i + 1)
else:
    exp.append(0)
    for i in range(1, n // 2 + 1):
        exp.append(2 * i)
        exp.append(2 * i)

a_sorted = sorted(a)

if a_sorted == exp:
    ans = 1
    for i in range(0, n // 2):
        ans *= 2
        if ans > 1000000007:
            ans -= 1000000007
    print(ans)
else:
    print(0)

Solution (Python):
def inpl(): return input().split()

n = int(input())
a = sorted(list(map(int, inpl())))
p = 10 ** 9 + 7

if a[0] == 0:
    st = 1
    next_value = 2
else:
    st = 0
    next_value = 1

ans = 1
found = False
for i in range(st, n):    
    if (next_value == a[i]):
        if found:
            next_value += 2
            found = False
            ans *= 2
            if ans > p:
                ans %= p
        else:
            found = True
    else:
        ans = 0
        break
print(ans)

Solution (Python):
from collections import defaultdict

n = int(input())
A = [int(i) for i in input().split()]
p = 10 ** 9 + 7

m = n % 2 == 0
cnt = defaultdict(int)

for a in A:
    if (a % 2 == 0) == m:
        print(0)
        exit()
    cnt[a] += 1

if cnt[0] > 1:
    print(0)
    exit(0)

del cnt[0]

for c in cnt.values():
    if c != 2:
        print(0)
        exit(0)

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

Solution (Python):
from collections import defaultdict

n = int(input())
A = [int(i) for i in input().split()]
p = 10 ** 9 + 7

m = n % 2 == 0
cnt = defaultdict(int)

for a in A:
    if (a % 2 == 0) == m:
        print(0)
        exit()
    cnt[a] += 1
    if cnt[a] > 2 or cnt[0] > 1:
        print(0)
        exit()

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

Solution (Python):


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

BN = [0] * (N//2+1)


for i in range(N):
    if N % 2 != 0:
        BN[N//2 - AN[i]//2] += 1
    else:
        BN[N//2 - (AN[i]//2+1)] += 1


ans = 0
for i in range(len(BN)):
    if BN[i] > 2 or N % 2 != 0 and BN[-1] > 1:
        print(0)
        exit()


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

Solution (Python):
mod=1000000007

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

t.sort()

f=1

if n%2==1:
    for i in range(n):
        if not t[i]//2==(i+1)//2 or t[i]%2==1:
            f=-1
else:
    for i in range(n):
        if not t[i]//2==i//2 or t[i]%2==0:
            f=-1

if f<0:
    print(0)
else:
    ans=1
    for i in range(n//2):
        ans=(ans*2)%mod
    print(ans)

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

if n%2 == 0:
    valid = True
    for i in range(n):
        if i%2 == 0: v = i+1
        else: v = i
        if a[i] != v:
            valid = False
            print(0)
            break
    if valid:
        print(2**(n//2)%MOD)

else:
    valid = True
    for i in range(n):
        if i%2 != 0: v = i+1
        else: v = i
        if a[i] != v:
            valid = False
            print(0)
            break
    if valid:
        print(2**(n//2)%MOD)

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

can = True
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:
            can = False
            break
else:
    possible_list = {i: True for i in range(0, n, 2)}
    if 0 not in a_dict:
        can = False
    elif a_dict[0] != 1:
        can = False
    else:
        a_dict[0] = 2
        for k, v in a_dict.items():
            if v != 2 or k not in possible_list:
                can = False
                break

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

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

candidates = []

for i in range(N // 2) :
    d = N - 1 - 2*i
    candidates.append(d)
    candidates.append(d)
    
if N % 2 != 0: 
    candidates.append(0)
    
if sorted(candidates) != sorted(a) :
    print(0)
else :
    c_dict = {}
    for c in candidates :
        if c in c_dict.keys() :
            c_dict[c] += 1
        else: 
            c_dict[c] = 1
            
    prod = 1
    for v in c_dict.values() :
        prod *= v
        
    print(prod % (10**9 + 7))

Solution (Python):
N = int(input())
A = list(map(int, input().split()))
cnt = {i : 0 for i in range(N)}
for a in A:
    cnt[a] += 1
exist_ans = True
if N % 2:
    if cnt[0] != 1:
        exiet_ans = False
    for i in range(2, N, 2):
        if cnt[i] != 2:
            exist_ans = False
else:
    for i in range(1, N, 2):
        if cnt[1] != 2:
            exist_ans = False
if exist_ans:
    print(2**(N//2) % (10**9 +7))
else:
    print(0)

Solution (Python):
from collections import Counter
n=int(input())
a=list(map(int, input().split()))
b=Counter(a)
ans=0
if n%2==1:
    for i in b:
        if i==0:
            if b[i]!=1:ans=1
        elif b[i]!=2 or i%2==1 or i>n:ans=1
else:
    for i in b:
        if b[i]!=2 or i%2==0 or i>n:ans=1
if ans==1:print(0)
else: print((2**(len(a)//2))%(10**9+7))

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

arr = map(int,raw_input().split())

sums = [0 for i in range(n)]

for i in range(n):
	sums[arr[i]] += 1


isprinted = False
mod = 1000000007
if n%2 == 1:
	if sums[0] == 1:
		for i in range(2,n,2):
			if sums[i] != 2:
				print 0
				isprinted = True
				break

		if not isprinted :
			print 2**((n-1)/2)%mod
	else :
		print 0

else :
	for i in range(1,n,2):
		if sums[i] != 2:
			print 0
			isprinted = True
			break

	if not isprinted:
		print 2**(n/2)%mod

Solution (Python):
from collections import Counter
n = int(input())
a = map(int, input().split())
c = Counter(a)
q,r = divmod(n, 2)
if r:
    b = [c[0] == 1]
    for i in range(1,q+1):
        b.append(c[i*2] == 2)
    if all(b):
        print(2**q%(10**9+7))
    else:
        print(0)
else:
    b = []
    for i in range(q):
        b.append(c[i*2+1] == 2)
    if all(b):
        print(2**q%(10**9+7))
    else:
        print(0)

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

def m():
    n = int(input())
    a = list(map(int, input().split()))
    a.sort()
    if a[0] == 0:
        tmp = 2
        for i in range(1, n, 2):
            for k in range(2):
                if a[i+k] != tmp:
                    return 0
            tmp += 2
        tmp -=2
        return (2 ** (tmp//2))%MOD

    if a[0] == 1:
        tmp = 1
        for i in range(0, n, 2):
            for k in range(2):
                if a[i+k] != tmp:
                    return 0
            tmp += 2
        tmp -= 1
        return (2 ** (tmp//2))%MOD
    return 0


print(m())

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

Solution (Python):
N = int(input())
evenFlg = False
flg = False
lastIndex = int((N - (N % 2))/2)
if N % 2 == 0: evenFlg = True
ary = [2 for i in range(lastIndex)]
l = list(map(int, input().split()))



if not evenFlg: ary.insert(0, 1)

for r in range(N):
    if evenFlg:
        l[r] = (l[r] - 1) / 2
    else:
        l[r] /= 2
    l[r] = int(l[r])
    ary[l[r]] -= 1
for k in range(lastIndex):
    if ary[k] != 0:
        flg = True
        break
ans = 0 if flg else (2**lastIndex) % (10**9 + 7)

print(ans)

Solution (Python):
def main():
    N = int(input())
    A = list(map(int, input().split()))
    A.sort()
    if N%2 == 1:
        if A[0] != 0:
            return 0
        for i in range(1,N,2):
            if (A[i]==i+1 and A[i+1]==i+1)==False:
                return 0
        return (2**(N//2))%(10**9+7)
    else:
        for i in range(0,N,2):
            if (A[i]==i+1 and A[i+1]==i+1)==False:
                return 0
        return (2**(N//2))%(10**9+7)

if __name__ == "__main__":
    print(main())

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

def is_valid(ctr):
    if N%2:
        if ctr[0] != 1:
            return False
        for i in range(2,N,2):
            if ctr[i] != 2:
                return False
    else:
        for i in range(1,N,2):
            if ctr[i] != 2:
                return False
    return True

if is_valid(ctr):
    MOD = 10**9+7
    print(2**(N//2) % MOD)
else:
    print(0)

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

flag = 1
if n % 2 == 1 :
    for i in range(0,n):
        if i == 0 :
            co = 0
            if x[i] == 0:
                x[i] = -1

        elif i != 0 and i <= n-2 and (i) % 2 ==1 :
            if x[i] == i+1 and x[i+1] == i+ 1 and (i+1) % 2 == 0:
                x[i] = -1
                x[i+1] = -1
        else:
            continue
else:
    for i in range(0,n):  
        if x[i] == i+1 and x[i+1] == i+ 1 and (i+1) % 2 == 1 and i <= n-2:
            x[i] = -1
            x[i+1] = -1
        else:
            continue
            
if list(set(x)) == [-1]:
    ans = 1
    if n >=2:
        for i in range(n // 2 ):
            ans = (ans * 2) % (10 ** 9 + 7)
        
    print(ans)
else:
    print(0)

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

    pos = True
    num_dict = {}
    if n % 2 == 0:
        for i in range(n):
            if a[i] % 2 == 0:
                pos = False
                break

            num_dict[a[i]] = num_dict.get(a[i], 0) + 1

    else:
        cnt0 = 0
        for i in range(n):
            if a[i] % 2 == 1:
                pos = False
                break
            elif a[i] == 0:
                cnt0 += 1
            else:
                num_dict[a[i]] = num_dict.get(a[i], 0) + 1

        if cnt0 != 1:
            pos = False

    for i in num_dict:
        if num_dict[i] != 2:
            pos = False

    if pos:
        com = 1
        for i in range(len(num_dict)):
            com *= 2
            if com >= 10 ** 9 + 7:
                com %= 10 ** 9 + 7

        print(com)
    else:
        print(0)


if __name__ == '__main__':
    main()

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

v = 1
idx = 0
if N%2 == 1:
    if A[0] != 0:
        print(0)
        exit()
    idx = 1
    v = 2
for i in range(N//2):
    for j in range(2):
        if A[idx+2*i+j] != v:
            print(0)
            exit()
    v += 2
print((2**(N//2))%(10**9+7))

Solution (Python):
n = int(input())
l = list(map(int, input().split()))
mod = 10**9+7
if n % 2 == 0 and len(set(l)) == n//2:
  print(2**(n//2)%mod)
elif not n % 2 == 0 and l.count(0) == 1:
  print(2**((n-1)//2)%mod)
else:
  print(0)

Solution (Python):
n = int(input())
a = sorted([int(i) for i in input().split()],reverse=True)
x = n+1

for i in range(len(a)):
  if i%2 ==0:
    x-=2
  if a[i] != x:
    print(0)
    break
else:
  print((2**(n//2))%(10**9 +7))

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

if a == able:
    r = n//2
    ans = 1
    for i in range(0,r):
        ans = ans * 2 % mod
    print(int(ans))
else:
    print(0)

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

if N%2==0:
    for k in B:
        if k%2==0 or B[k]!=2:
            print(0)
            exit(0)
else:
    if B[0] != 1:
        print(0)
        exit(0)
    B[0] = 2
    for k in B:
        if k%2==1 or B[k]!=2:
            print(0)
            exit(0)

ans = 1
for k in range(N//2):
    ans *= 2
    ans %= 10**9+7
print(ans)

Solution (Python):
N = int(input())
A = list(map(int, input().split(' ')))
q = {}
flag = 0
for i in range(N):
    if A[i] in q:
        q[A[i]] += 1
    else:
        q[A[i]] = 1
if N % 2 == 0:
    even = [2*i+1 for i in range(N // 2)]
    for i in even:
        if i not in q.keys():
            flag = 1
            break
        elif q[i] != 2:
            flag = 1
            break
    if flag == 1:
        print(0)
    else:
        print(pow(2, len(q.keys())) % 1000000007)
else:
    odd = [2*i for i in range((N+1) // 2)]
    for i in odd:
        if i not in q.keys():
            flag = 1
            break
        elif i == 0 and q[i] != 1:
            flag = 1
            break
        elif i != 0 and q[i] != 2:
            flag = 1
            break
    if flag == 1:
        print(0)
    else:
        print(pow(2, (len(q.keys()) - 1)) % 1000000007)

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

def beki(n):
    ans = 1
    for _ in range(int(n)):
        ans = (ans * 2) % (10 ** 9 + 7)
    return int(ans)

if n % 2 == 0:
    hikaku = []
    for i in range(1, n, 2):
        hikaku += [i, i]
    if sorted(a) == hikaku:
        print(beki(n / 2))
    else:
        print(0)

elif n == 1:
    if a == [0]:
        print(1)
    else:
        print(0)
else:
    hikaku = [0]
    for i in range(2, n, 2):
        hikaku += [i, i]
    if sorted(a) == hikaku:
        print(beki((n - 1) / 2))
    else:
        print(0)

Solution (Python):
N=int(input())
s=list(map(int,input().split()))
if N%2==1:
    s.remove(0)
s=list(sorted(s))
if s[0::2]==s[1::2]:
    print((2**((len(s))//2))%(10**9+7))
else:
    print(0)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
mod=10**9+7
from collections import Counter
data=Counter(a)
if n%2==1:
    if 0 not in a:
        print(0)
        exit()
    else:
        a.remove(0)
        data=Counter(a)
        for i in data.values():
            if i!=2:
                print(0)
                exit()
    print((2**(n//2))%mod)
else:
    for i in data.values():
        if i!=2:
            print(0)
            exit()
    print((2**(n//2))%mod)

Solution (Python):
n=int(input())
a=list(map(int,input().split()))
mod=10**9+7
from collections import Counter
data=Counter(a)
if n%2==0:
    if 0  in a:
        print(0)
        exit()
    else:
        for i in data.values():
            if i!=2:
                print(0)
                exit()
    print((2**(n//2))%mod)
else:
    if a.count(0)!=1:
        print(0)
        exit()
    else:
        a.remove(0)
        data=Counter(a)
        for i in data.values():
            if i!=2:
                print(0)
                exit()
    print((2**(n//2))%mod)

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

C = Counter(A).most_common()
p = 0
for k,v in C:
    if v==1 and k==0 and N%2==1:
        continue
    elif v==2:
        p += 1
        continue
    else:
        p = 0
        break
if N==1 and A==[0]:
    print(1)
else:
    print(p if p==0 else (2**p)%(10**9+7))

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

C = Counter(A).most_common()
p = 0
for k,v in C:
    if v==1 and k==0 and N%2==1:
        continue
    elif v==2:
        p += 1
        continue
    else:
        p = 0
        break
if N==1:
    print(1)
else:
    print(p if p==0 else (2**p)%(10**9+7))

Solution (Python):
from collections import Counter

N = int(input())
src = list(map(int,input().split()))
ctr = Counter(src)

def valid():
    if N%2:
        if ctr[0] != 1: return False
        i = 2
        while i <= N:
            if ctr[i] != 2: return False
            i += 2
    else:
        i = 1
        while i <= N:
            if ctr[i] != 2: return False
            i += 2
    return True

MOD = 10**9+7
print(2**(N//2) % MOD if valid() else 0)

Solution (Python):
def calc(n):
	ans = 1
	for i in range(0, n):
		ans = ans * 2
		if ans >= 1000000007:
			ans = ans - 1000000007
	return ans

def judge(n, lst):
	start = 0
	if n%2 == 1:
		if lst[0] != 0: return False
		else: start = 1
	for i in range(0, n/2):
		if lst[2*i+start] != lst[2*i+start+1]:
			return False
		elif lst[2*i+start] != 2*i+1+start:
			return False
	return True

n = int(raw_input())
inpt = map(int, raw_input().split())
inpt.sort()

if judge(n, inpt):
	print calc(n/2)
else:
	print 0

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

Solution (Python):
from collections import defaultdict
n = int(input())
a = list(map(int, input().split()))
di = defaultdict(int)
right = True
for i in range(n):
    if n < a[i]:
        right = False
    if (n%2==0 and a[i]%2==1):
        di[a[i]] += 1
    elif (n%2==1 and a[i]%2==0):
        di[a[i]] += 1
    if 2 < di[a[i]]:
        right = False
    if a[i]==0 and di[a[i]]>1:
        right = False
    if n%2==0 and a[i]%2==0:
        right = False
    elif n%2==1 and a[i]%2 ==1:
        right = False

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

Solution (Python):
N=int(input())
A=sorted([int(i) for i in input().split()],reverse=True)


B=[]
for i in range(N//2):
    for p in [0,1]:
        B.append(N-1-2*i)
if N%2==1:
    B.append(0)
for i in range(N):
    if A[i]!=B[i]:
        print(0)
        exit()
M=1
P=10**9+7
for i in range(N//2):
	M=(2*M)%P
print(M)