python RE 求助

代码如下

dir = {}
n = int(input())
for i in range(n):
    dir[i + 1] = []
    m = input()
    for j in m:
        if j != " " and j != "0":
            dir[i + 1].append(int(j))
ans = []
while len(ans) < n:
    for i in dir.keys():
        if dir[i] == []:  # 出度为零
            dir[i] = -1  # 删除结点
            ans.append(str(i))
            continue
        if dir[i] == -1:  # 结点被删除
            continue
        num = 0
        for j in dir[i]:
            if dir[j] != -1:  # 出度不为零
                num = 1
                break
        if num == 0:  # 出度为零
            dir[i] = -1  # 删除结点
            ans.append(str(i))
print(" ".join(ans[::-1]))  # 逆序输出

除最后一个点，全RE了，不解