Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    for i in range(ln - 1, 1, -2):
        if not s.count(i) == 2:
            return False
    if ln % 2 == 0:
        if not s.count(1) == 2:
            return False
    else:
        if not s.count(0) == 1:
            return False

    return True


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)


Fixed submission:
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = sorted(list(range(ln - 1, 1, -2)) * 2)
    if ln % 2 == 0:
        check.insert(0, 1)
        check.insert(0, 1)
    else:
        check.insert(0, 0)

    return sorted(s) == check

    # for i in range(ln - 1, 1, -2):
    #     if not s.count(i) == 2:
    #         return False
    # if ln % 2 == 0:
    #     if not s.count(1) == 2:
    #         return False
    # else:
    #     if not s.count(0) == 1:
    #         return False

    # return True


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = [s.count(i) == 2 for i in range(ln - 1, 1, -2)]
    if ln % 2 == 0:
        check.append(s.count(1) == 2)
    else:
        check.append(s.count(0) == 1)

    return all(check)


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)


Fixed submission:
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = sorted(list(range(ln - 1, 1, -2)) * 2)
    if ln % 2 == 0:
        check.insert(0, 1)
        check.insert(0, 1)
    else:
        check.insert(0, 0)

    return sorted(s) == check

    # for i in range(ln - 1, 1, -2):
    #     if not s.count(i) == 2:
    #         return False
    # if ln % 2 == 0:
    #     if not s.count(1) == 2:
    #         return False
    # else:
    #     if not s.count(0) == 1:
    #         return False

    # return True


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)

Buggy python submission (verdict: Time Limit Exceeded):
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = [s.count(i) == 2 for i in range(ln - 1, 1, -2)]
    if ln % 2 == 0:
        check.append(s.count(1) == 2)
    else:
        check.append(s.count(0) == 1)

    return all(check)


ans = 2 ** (n // 2) if is_satisfied(a) else 0
print(ans)


Fixed submission:
n = int(input())
a = [int(x) for x in input().split()]

def is_satisfied(s):
    ln = len(s)
    check = sorted(list(range(ln - 1, 1, -2)) * 2)
    if ln % 2 == 0:
        check.insert(0, 1)
        check.insert(0, 1)
    else:
        check.insert(0, 0)

    return sorted(s) == check

    # for i in range(ln - 1, 1, -2):
    #     if not s.count(i) == 2:
    #         return False
    # if ln % 2 == 0:
    #     if not s.count(1) == 2:
    #         return False
    # else:
    #     if not s.count(0) == 1:
    #         return False

    # return True


ans = 2 ** (n // 2) % (10 ** 9 + 7)
print(ans if is_satisfied(a) else 0)