simple topological sort

timus_1022.py

#!/usr/bin/python3
"""
TIMUS 1022

ACCEPTED

2014-03-23
"""
q = set()
n = int(input())
ch = [[] for i in range(0, n)]
pa = [0 for i in range(0, n)]
ans = []

for i in range(0, n):
    tc = [int(x) for x in input().split(' ')]
    for t in tc:
        if t:
            ch[ i ].append(t - 1)
            pa[ t - 1 ] += 1

for i in range(0, n):
    if pa[ i ]:
        q.add(i)

while len(ans) != n:
    t = q.pop()
    ans.append(t)
    for c in ch[t]:
        pa[c] -= 1
        if pa[c] and c not in ans:
            q.add(c)

print (" ".join([str(a + 1) for a in ans]))