Buggy python submission (verdict: Runtime Error):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    for i in range(1,n//2+1):
        if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
            None
        else:
            out = 1
elif a[0] == 1:
    for i in range(n//2):
        if a[2*i] == a[2*i+1] == 2*i+1:
            None
        else:
            out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Buggy python submission (verdict: Runtime Error):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    for i in range(1,n//2+1):
        if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
            None
        else:
            out = 1
elif a[0] == 1:
    for i in range(n//2):
        if a[2*i] == a[2*i+1] == 2*i+1:
            None
        else:
            out = 1
else:
    out = 1
if out:
    print(0)
else:
    print(2**(n//2)%(10**9+7))


Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Buggy python submission (verdict: Runtime Error):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    for i in range(1,n//2+1):
        if a[2*i-1] == a[2*i] == 2*i:
            None
        else:
            out = 1
elif a[0] == 1:
    for i in range(n//2):
        if a[2*i] == a[2*i+1] == 2*i+1:
            None
        else:
            out = 1
else:
    out = 1
if out:
    print(0)
else:
    print(2**(n//2)%(10**9+7))

Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Buggy python submission (verdict: Runtime Error):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    for i in range(1,n//2+1):
        if a[2*i-1] == a[2*i] == 2*i:
            None
        else:
            out = 1
elif a[0] == 1:
    for i in range(n//2):
        if a[2*i] == a[2*i+1] == 2*i+1:
            None
        else:
            out = 1
else:
    out = 1
if out:
    print(0)
else:
    print(2**(n//2))

Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Buggy python submission (verdict: Runtime Error):
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if a[0] == 0:
    for i in range(1,n//2+1):
        if a[2*i-1] == a[2*i] == 2*i:
            None
        else:
            out = 1
elif a[0] == 1:
    for i in range(n//2):
        if a[2*i] == a[2*i+1] == 2*i+1:
            None
        else:
            out = 1
else:
    out = 1
if out:
    print(0)
else:
    print(2**(n//2))

Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)

Buggy python submission (verdict: Time Limit Exceeded):
import sys
n = int(input())
a = [int(i) for i in input().split()]
for i in range(n):
    if a.count(i)>=3:
        print(0)
        sys.exit()
if a.count(0) >= 2:
    print(0)
    sys.exit()
if 0 in a:
    a.remove(0)
b = set(a)
print(2**(len(b)))


Fixed submission:
n = int(input())
a = [int(i) for i in input().split()]
a.sort()
out = 0
if n == 1:
    if a[0] != 0:
        out = 1
elif a[0] == 0:
    if n%2 == 0:
        out = 1
    else:
        for i in range(1,n//2+1):
            if a[2*i-1] == a[2*i] and a[2*i] == 2*i:
                None
            else:
                out = 1
elif a[0] == 1:
    if n%2 == 1:
        out = 1
    else:
        for i in range(n//2):
            if a[2*i] == a[2*i+1] == 2*i+1:
                None
            else:
                out = 1
else:
    out = 1
if out:
    print(0)
else:
    a = 1
    for i in range(n//2):
        a *= 2
        a = a%(10**9+7)
    print(a)