Problem p03142 (python)

Fixed submission:
from collections import deque
N, M = map(int, input().split())
graph = [] 
for i in range(N + M - 1):
    a, b = map(int, input().split())
    graph += [[a,b]]

path = [[] for i in range(N)]  
parent = [[] for i in range(N)]
ans = [-1 for i in range(N)]
for p in graph:
    parent[p[1]-1] += [p[0]-1]
    path[p[0]-1] += [p[1]-1]

root = -1
for i in range(N):
    if parent[i] == []:
        root = i
        parent[i] = [-1]
visited = [0 for i in range(N)]
visited[root] = 1

que = deque()
for v in path[root]:
    ans[v] = root
    if len(parent[v]) > 1:
        parent[v].remove(root) 
    else: que.append([root, v])
while que:
    u, V = que.popleft()
    for v in path[V]:
        if len(parent[v]) > 1:
            parent[v].remove(V)
        else:
            que.append([V, v])
for i in range(N):
    print(parent[i][0]+1)

Buggy submission (verdict: Runtime Error):
from collections import deque
N, M = map(int, input().split())
graph = [] 
for i in range(N + M - 1):
    a, b = map(int, input().split())
    graph += [[a,b]]

path = [[] for i in range(N)]  
parent = [[] for i in range(N)]
ans = [-1 for i in range(N)]
for p in graph:
    parent[p[1]-1] += [p[0]-1]
    path[p[0]-1] += [p[1]-1]

root = -1
for i in range(N):
    if parent[i] == []:
        root = i
        parent[i] = [-1]
visited = [0 for i in range(N)]
visited[root] = 1

que = deque()
for v in path[root]:
    ans[v] = root
    que.append([root, v])
    if len(parent[v]) > 1:
        parent[v].remove(root) 
while que:
    u, V = que.popleft()
    for v in path[V]:
        if len(parent[v]) > 1:
            parent[v].remove(V)
        else:
            que.append([V, v])
for i in range(N):
    print(parent[i][0]+1)

Buggy submission (verdict: Runtime Error):
from collections import deque
N, M = map(int, input().split())
graph = [] 
for i in range(N + M - 1):
    a, b = map(int, input().split())
    graph += [[a,b]]

path = [[] for i in range(N)]  
parent = [[] for i in range(N)]
ans = [-1 for i in range(N)]
for p in graph:
    parent[p[1]-1] += [p[0]-1]
    path[p[0]-1] += [p[1]-1]

root = -1
for i in range(N):
    if parent[i] == []:
        root = i
        parent[i] = [-1]
visited = [0 for i in range(N)]
visited[root] = 1

que = deque()
for v in path[root]:
    ans[v] = root
    que.append([root, v])
    if len(parent[v]) > 1:
        parent[v].remove(root) 
while que:
    u, V = que.popleft()
    for v in path[V]:
        if visited[v] == 0:
            if len(parent[v]) > 1:
                parent[v].remove(V)
            else:
                visited[v] = 1
                que.append([V, v])
for i in range(N):
    print(parent[i][0]+1)

Buggy submission (verdict: Runtime Error):
from collections import deque
N, M = map(int, input().split())
graph = [] 
for i in range(N + M - 1):
    a, b = map(int, input().split())
    graph += [[a,b]]

path = [[] for i in range(N)]  
parent = [[] for i in range(N)]
ans = [-1 for i in range(N)]
for p in graph:
    parent[p[1]-1] += [p[0]-1]
    path[p[0]-1] += [p[1]-1]

root = -1
for i in range(N):
    if parent[i] == []:
        root = i
        parent[i] = [-1]
visited = [0 for i in range(N)]
visited[root] = 1

que = deque()
for v in path[root]:
    ans[v] = root
    que.append([root, v])
    if len(parent[v]) > 1:
        parent[v].remove(root) 
while que:
    u, V = que.popleft()
    for v in path[V]:
        if visited[v] == 0:
            visited[v] = 1
            que.append([V, v])
        if len(parent[v]) > 1:
            parent[v].remove(V)
for i in range(N):
    print(parent[i][0]+1)