백준 문제 2252

#include<stdio.h>
#include <stdio.h>
#include <iostream>
#include <queue>
#include <vector>
#include <functional>

using namespace std;
vector<int> adj[32001];
queue<int> q;
int indegree[32001];

int main(){
	int N, M;
	cin >> N >> M; 
	while (M--){
		int a, b;
		scanf("%d%d", &a, &b);
		adj[a].push_back(b);
	   indegree[b]++;
	}

	for (int i = 1; i <= N; ++i){
		if (indegree[i] == 0)
		q.push(i);
	}
	while (!q.empty())
	{
		int c = q.front();
		printf("%d ", c);
		q.pop();
		for (int i : adj[c])
		{
			--indegree[i];
			if (indegree[i] == 0)
				q.push(i);
		}
	}
}