Buggy python submission (verdict: Time Limit Exceeded):
N = int(input())
A = list(map(int,input().split()))
Nc = 0
e = 0
B = []
A.sort()
if N % 2 == 0:
    for i in range(1, N//2 + 1):
        B = B + [2*i - 1, 2*i -1]
    if A == B:
        Nc = 2**(N//2)
else:
    for i in range(1, ((N-1)//2) + 1):
        B = B + [2*i, 2*i]
    B = [0] + B
    if A == B:
        Nc = 2**((N-1)//2)

print(Nc%1000000007)

Fixed submission:
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)

Buggy python submission (verdict: Time Limit Exceeded):
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
for i in range(N):
    if (N-A[i]-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        for i in range(N-1):
                if A.count(i+1) == 2:
                    Nc *= 2
                elif A.count(i+1) ==0:
                    Nc *= 1
                else:
                    Nc *= 0
                    break

print(Nc%1000000007)

Fixed submission:
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)

Buggy python submission (verdict: Runtime Error):
N = int(input())
A = list(map(int,input().split()))
Nc = 1
if A.count(0) >= 2:
    Nc *= 0
else:
    for i in range(N):
        if (N-A[i]-1) >= 0:
                if A.count(i+1) == 2:
                    Nc = Nc*2
                elif A.count(i+1) == 0:
                else:
                    Nc *= 0
                    break
        else:
            Nc *= 0
            break

print(Nc%1000000007)

Fixed submission:
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)

Buggy python submission (verdict: Time Limit Exceeded):
N = int(input())
A = list(map(int,input().split()))
Nc = 1
if A.count(0) >= 2:
    Nc *= 0
else:
    for i in range(N):
        if (N-A[i]) >= 1:
                if A.count(i+1) == 2:
                    Nc = Nc*2%1000000007
                elif A.count(i+1) == 0:
                    Nc *= 1
                else:
                    Nc *= 0
                    break
        else:
            Nc *= 0
            break

print(Nc)

Fixed submission:
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)

Buggy python submission (verdict: Runtime Error):
N = int(input())
A = list(map(int,input().split()))
Nc = 1
if A.count(0) >= 2:
    Nc *= 0
else:
    for i in range(N):
        if (N-A[i]) >=1
                if A.count(i+1) == 2:
                    Nc = Nc*2%1000000007
                elif A.count(i+1) == 0:
                    Nc *= 1
                else:
                    Nc *= 0
                    break
        else:
            Nc *= 0
            break

print(Nc)


Fixed submission:
N = int(input())
A = list(map(int,input().split()))
Nc = 1
e = 0
B = [0]*N
for i in A:
    if (N-i-1) < 0:
        e = 1
        Nc = 0
        break
if e ==0:
    if A.count(0) >= 2:
        Nc *= 0
    else:
        if A.count(0) == 1:
            A.remove(0)
        for i in A:
            B[i] = B[i] + 1
        for i in B:
            if i == 2:
                Nc *= 2
            elif i == 0:
                Nc *= 1
            else:
                Nc *= 0
                break
print(Nc%1000000007)