Course Schedule

import sys
from collections import deque, defaultdict, Counter
from heapq import heappush, heappop, heapify
from bisect import bisect_left, bisect_right
from itertools import permutations, combinations, product, accumulate, groupby
from functools import lru_cache, cmp_to_key, reduce
from math import gcd, isqrt, comb, inf, pi, sqrt, atan2, hypot


def main():
    data = sys.stdin.buffer.read().split(); idx = 0
    n = int(data[idx]); idx += 1
    m = int(data[idx]); idx += 1
    # a = list(map(int, data[idx:idx + n])); idx += n
    after = [[] for _ in range(n+1)]
    indeg = [0] * (n + 1)

    # before = [[] for _ in range(n)]
    # start = set(range(1, n+1))
    for _ in range(m):
        a = int(data[idx]); idx += 1
        b = int(data[idx]); idx += 1
        after[a].append(b)
        indeg[b] += 1
        # if b in start: start.remove(b)
    
    out = []
    # rem = set(range(1, n+1))

    # for i in range(n):
    #     if after
    # if not start:
    #     print("IMPOSSIBLE")

    # # start = 1
    # idx = start.pop()
    # for i in range(1,n+1):
    #     if :


    # while rem:
    #     out.append(idx)
    q = deque(i for i in range(1, n + 1) if indeg[i] == 0)
    while q:
        u = q.popleft()
        out.append(u)
        for v in after[u]:
            indeg[v] -= 1
            if indeg[v] == 0:
                q.append(v)



    if len(out) < n:
        print("IMPOSSIBLE")
        exit()
    print(" ".join(map(str, out)))
    # sys.stdout.write("\n".join(map(str, out)) + "\n")


main()

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: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED