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

a = list(map(int,input().split()))

result = False

if n % 2 == 0:
    if len(a) == n and sum(a) == n*n/2:
        for i in range(n-1, -1, -2):
            if i not in set(a):break
        result = True

else:
    if len(a) == n and sum(a) == (n+1)*(n-1)/2:
        for i in range(n-1, -1, -2):
            if i not in set(a):break
        result = True
        
if result: print(2**int(n/2) % (10**9+7))
else:print(0)
  

Fixed submission:
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)

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

a = list(map(int,input().split()))

result = False

if len(set(a)) == int((n+1)/2) and sum(a)==int(n/2)*int((n+1)/2)*2:
    for i in range(n-1, -1, -2):
        if i not in set(a):
            result = False
            break
    result = True

if result:print(2**int(n/2) % (10**9 + 7))
else:
    print(0)

Fixed submission:
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)

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

a = list(map(int,input().split()))

result = -1

for i in range(n-1, -1, -2):
    if i != 0 and a.count(i) != 2 or i == 0 and a.count(i) != 1:
        result = 0
        break

if result == 0:print(result)
else:
    print(2**int(n/2) % (10**9 + 7))


Fixed submission:
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)

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

a = list(map(int,input().split()))

result = -1

for i in range(n-1, -1, -2):
    if i != 0 and a.count(i) != 2 or i == 0 and a.count(i) != 1:
        result = 0
        break

if result == 0:print(result)
else:
    print(2**int(n/2) % (10**9 + 7))


Fixed submission:
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)

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

a = list(map(int,input().split()))

result = -1

for i in range(n-1, -1, -2):
    check = 0
    for ii in range(n):
        if a[ii] == i: check += 1
    if i != 0 and check != 2:
        result = 0
        break
    elif i == 0 and check != 1:
        result = 0
        break
if result != 0:
    result = 2**int(n / 2) % (10 ** 9 + 7)

print(result)
    
        
        

Fixed submission:
from  collections import Counter

n =int(input())

a = list(input().rstrip().split())

count_num = Counter(a)

result = True

if len(a) == n:
    if n % 2 == 0:
        for i in range(n-1, -1, -2):
            if count_num[str(i)] ==2:
                continue
            else:
                result = False
                break

    else:
        if count_num['0'] == 1:
            for i in range(n-1, 1, -2):                
                if count_num[str(i)] ==2:continue
                else:
                    result = False
                    break
        else:result=False

if result: print(2**int(n/2) % (10**9+7))
else:print(0)