Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
if n % 2:
    if a.count(0) != 1:
        print(0)
        exit()
    for i in range(2, n, 2):
        if a.count(i) != 2:
            print(0)
            exit()
else:
    if a.count(1) != 2:
        print(0)
        exit()
    for i in range(1, n, 2):
        if i == 1:
            continue
        if a.count(i) != 2:
            print(0)
            exit()
mod = 10 ** 9 + 7
print((2 ** (n // 2)) % mod)

Fixed submission:
import collections

n = int(input())
a = list(map(int, input().split()))
ac = collections.Counter(a)
if n % 2 == 1:
    for i in ac:
        if i == 0:
            if ac[i] != 1:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    for i in ac:
        if i == 0:
            if ac[i] != 0:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
if n % 2:
    if a.count(0) != 1:
        print(0)
        exit()
    for i in range(2, n, 2):
        if a.count(i) != 2:
            print(0)
            exit()
else:
    if a.count(1) != 2:
        print(0)
        exit()
    for i in range(1, n, 2):
        if i == 1:
            continue
        if a.count(i) != 2:
            print(0)
            exit()
mod = 10 ** 9 + 7
ans = 1
for i in range(n // 2):
    ans = (ans % mod) * 2
print(ans % mod)

Fixed submission:
import collections

n = int(input())
a = list(map(int, input().split()))
ac = collections.Counter(a)
if n % 2 == 1:
    for i in ac:
        if i == 0:
            if ac[i] != 1:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    for i in ac:
        if i == 0:
            if ac[i] != 0:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
if n % 2:
    if a.count(0) != 1:
        print(0)
        exit()
    for i in range(2, n, 2):
        if a.count(i) != 2:
            print(0)
            exit()
else:
    if a.count(1) != 2:
        print(0)
        exit()
    for i in range(1, n, 2):
        if i == 1:
            continue
        if a.count(i) != 2:
            print(0)
            exit()
print(2 ** (n // 2))

Fixed submission:
import collections

n = int(input())
a = list(map(int, input().split()))
ac = collections.Counter(a)
if n % 2 == 1:
    for i in ac:
        if i == 0:
            if ac[i] != 1:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    for i in ac:
        if i == 0:
            if ac[i] != 0:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
if n % 2:
    if a.count(0) != 1:
        print(0)
        exit()
    for i in range(n):
        if i % 2 or i == 0:
            continue
        if a.count(i) != 2:
            print(0)
            exit()
else:
    if a.count(1) != 2:
        print(0)
        exit()
    for i in range(n):
        if i % 2 == 0 or i == 1:
            continue
        if a.count(i) != 2:
            print(0)
            exit()
print(2 ** (n // 2))

Fixed submission:
import collections

n = int(input())
a = list(map(int, input().split()))
ac = collections.Counter(a)
if n % 2 == 1:
    for i in ac:
        if i == 0:
            if ac[i] != 1:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    for i in ac:
        if i == 0:
            if ac[i] != 0:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = list(map(int, input().split()))
if n % 2 == 1:
    if a.count(0) > 1:
        print(0)
    else:
        a.remove(0)
        for i in list(set(a)):
            if a.count(i) != 2:
                print(0)
                exit()
        print(2 ** ((n - 1) // 2))
else:
    if a.count(0) > 0:
        print(0)
    else:
        for i in list(set(a)):
            if a.count(i) != 2:
                print(0)
                exit()
        print(2 ** (n // 2))

Fixed submission:
import collections

n = int(input())
a = list(map(int, input().split()))
ac = collections.Counter(a)
if n % 2 == 1:
    for i in ac:
        if i == 0:
            if ac[i] != 1:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))
else:
    for i in ac:
        if i == 0:
            if ac[i] != 0:
                print(0)
                exit()
        else:
            if ac[i] != 2:
                print(0)
                exit()
    print((2 ** (n // 2)) % (10 ** 9 + 7))