백준 2252번 : 줄 세우기

문제 링크 : www.acmicpc.net/problem/2252

내 풀이(2021.2.10.) : 위상 정렬

#include <iostream>
#include <queue>
#include <vector>

using namespace std;

int N, M;
int indegree[32001];
vector<int> pointing[32001];
vector<int> ordered;

void topology_sort() {
	queue<int> q;
	for (int i = 1; i <= N; i++) {
		if (indegree[i] == 0) {
			q.push(i);
		}
	}
	while (!q.empty()) {
		int out = q.front(); q.pop();
		ordered.push_back(out);
		for (int con : pointing[out]) {
			indegree[con]--;
			if (indegree[con] == 0) {
				q.push(con);
			}
		}
	}
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	cin >> N >> M;
	for (int i = 0; i < M; i++) {
		int a, b; cin >> a >> b;
		pointing[a].push_back(b);
		indegree[b]++;
	}
	
	topology_sort();

	for (int i = 0; i < ordered.size(); i++) {
		cout << ordered[i] << ' ';
	}

	return 0;
}