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

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h..most_common():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1000000007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0) 

Fixed submission:
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.items():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1000000007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0)

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

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.items():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1_000_000_007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0) 

Fixed submission:
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.items():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1000000007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0)

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

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.most_common():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1_000_000_007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0) 

Fixed submission:
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.items():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1000000007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0)

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

n = int(input())
a = map(int, input().split())
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.most_common():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1_000_000_007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0) 

Fixed submission:
from collections import Counter

n = int(input())
a = list(map(int, input().split()))
h = Counter()
for x in a:
    h[x] += 1
f = True
for k, v in h.items():
    if n % 2 == 1 and k == 0:
        if v != 1:
            f = False
            break
    elif v != 2:
        f = False
        break
MOD = 1000000007
def mpow(n, p, mod):
    r = 1
    while p > 0:
        if p & 1 == 1:
            r = r * n % mod
        n = n * n % mod
        p >>= 1
    return r
print(mpow(2, int(n / 2), MOD) if f else 0)