每日一道算法题之拓扑排序之按照最小字典输出

import java.io.*;
import java.util.*;

public class Main {

    public static int n = 100001;
    public static int m = 100001;

    public static ArrayList<ArrayList<Integer>> graph = new ArrayList<>();

    public static PriorityQueue<Integer> heap = new PriorityQueue<>();

    public static int[] indegree = new int[n];

    public static int[] ans = new int[n];

    public static int cnt = 0;

    public static void build() {
        graph.clear();
        heap.clear();
        cnt = 0;
        for (int i = 0; i < n; i++) {
            graph.add(new ArrayList<>());
        }
    }

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StreamTokenizer in = new StreamTokenizer(br);
        PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
        while (in.nextToken() != StreamTokenizer.TT_EOF) {
            n = (int) in.nval + 1;
            in.nextToken();
            m = (int) in.nval;
            build();
            for (int i = 0, from, to; i < m; i++) {
                in.nextToken();
                from = (int) in.nval;
                in.nextToken();
                to = (int) in.nval;
                addEdge(from, to);
                indegree[to]++;
            }
            topoSort();
            for (int i = 0; i < n; i++) {
                out.print(ans[i] + " ");
            }
            out.println(ans[n - 1]);
        }
        out.flush();
        out.close();
        br.close();
    }

    private static void topoSort() {
        for (int i = 1; i < n; i++) {
            if (indegree[i] == 0) {
                heap.add(i);
            }
        }
        while (!heap.isEmpty()) {
            int cur = heap.poll();
            ans[cnt++] = cur;
            for (int i : graph.get(cur)) {
                indegree[i]--;
                if (indegree[i] == 0) {
                    heap.add(i);
                }

            }
        }

    }

    private static void addEdge(int from, int to) {
        graph.get(from).add(to);
    }
}