Buggy python submission (verdict: Runtime Error):
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n//2
ca = Counter(a)

if n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (1e9 + 7)
    print(int(ans))
elif n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (1e9 + 7)
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)

Buggy python submission (verdict: Runtime Error):
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n//2
ca = Counter(a)

if n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = 2 ** m % (1e9 + 7)
    print(int(ans))
elif n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = 2 ** m % (1e9 + 7)
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)

Buggy python submission (verdict: Runtime Error):
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n//2
ca = Counter(a)

if n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = 2 ** m % (1e9 + 7)
    print(int(ans))
elif n % 2 == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = 2 ** m % (1e9 + 7)
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = input().split()

flag = True
if n % 2 == 0:
    for i in range(int(n/2)):
        if a.count(str(i*2 + 1)) == 2:
            pass
        else:
            flag = False
            break
    ans = 2**(n/2) % (1e9 + 7)

else:  # n % 2 == 1
    if a.count('0') == 1:
        for i in range(int((n - 1) / 2)):
            if a.count(str((i + 1) * 2)) == 2:
                pass
            else:
                flag = False
                break
    else:
        flag = False

    ans = 2**((n-1)/2) % (1e9 + 7)

if flag:
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = input().split()

flag = True
if n % 2 == 0:
    for i in range(int(n/2)):
        if a.count(str(i*2 + 1)) == 2:
            pass
        else:
            flag = False
            break
    ans = 2**(n/2) % (10**9 + 7)

else:  # n % 2 == 1
    if a.count('0') == 1:
        for i in range(int((n - 1) / 2)):
            if a.count(str((i + 1) * 2)) == 2:
                pass
            else:
                flag = False
                break
    else:
        flag = False

    ans = 2**((n-1)/2) % (10**9 + 7)

if flag:
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = input().split()

flag = True
if n % 2 == 0:
    for i in range(int(n/2)):
        if a.count(str(i*2 + 1)) == 2:
            pass
        else:
            flag = False
    ans = 2**(n/2) % (10**9 + 7)

else:  # n % 2 == 1
    if a.count('0') == 1:
        pass
    else:
        flag = False
    for i in range(int((n-1)/2)):
        if a.count(str((i+1)*2)) == 2:
            pass
        else:
            flag = False
    ans = 2**((n-1)/2) % (10**9 + 7)

if flag:
    print(int(ans))
else:
    print(0)


Fixed submission:

from collections import Counter

n = int(input())
a = list(map(int, input().split()))
m = n // 2
ca = Counter(a)

if n % 2 == 1 and ca[0] == 1 and all(ca[(i+1)*2] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
elif n % 2 == 0 and all(ca[i*2 + 1] == 2 for i in range(m)):
    ans = (2 ** m) % (10 ** 9 + 7)
    print(ans)
else:
    print(0)