Course Schedule

import sys
input = sys.stdin.readline
n, m = map(int, input().split())

def topo_sort():
    graph = [[] for _ in range(n+1)]
    for _ in range(m):
        u, v = map(int, input().split())
        graph[u].append(v)
    order = []
    visited = [0]*(n+1)
    def dfs(u):
        visited[u]=-1
        for v in graph[u]:
            if visited[v] ==-1:
                return False 
            if visited[v]==0 and not dfs(v):
                return False
        visited[u] = True
        order.append(u)
        return True
    for node in range(1,n+1):
        if visited[node] ==0 and not dfs(node):
            print("IMPOSSIBLE")
            return []
    return order[::-1]
print(*topo_sort())

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: RUNTIME ERROR

Traceback (most recent call last):
  File "/box/input/code.py", line 27, in <module>
    print(*topo_sort())
  File "/box/input/code.py", line 23, in topo_sort
    if visited[node] ==0 and not dfs(node):
  File "/box/input/code.py", line 17, in dfs
    if visited[v]==0 and not dfs(v):
  File "/box/input/code.py", line 17, in dfs
    if visited[v]==0 and not dfs(v):
  File "/box/input/code.py", line 17, in dfs
    if visited[v]==0 and not dfs(v):
  [Previous line repeated 1685 more times]
  File "/box/input/code.py", line 15, in dfs
    if visited[v] ==-1:
RecursionError: maximum recursion depth exceeded

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED