백준 2252

package baekjoon.위상정렬;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.StringTokenizer;

class Main2252 {

   static int N, M;
   static StringBuilder sb = new StringBuilder();
   static int[] indeg;
   static ArrayList<Integer>[] g;

   public static void main(String[] args) throws Exception {
      input();
      go();

   }

   private static void go() {
      Deque<Integer> q = new LinkedList<>();
      for (int i = 1; i <= N; i++) {
         if (indeg[i] == 0)
            q.add(i);
      }
      while (!q.isEmpty()) {
         int x = q.poll();
         sb.append(x).append(' ');
         for (int y : g[x]) {
            indeg[y]--;
            if (indeg[y] == 0)
               q.add(y);
         }
      }
      System.out.println(sb);
   }

   private static void input() throws IOException {
      BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
      StringTokenizer st = new StringTokenizer(br.readLine());
      N = Integer.parseInt(st.nextToken());
      M = Integer.parseInt(st.nextToken());
      g = new ArrayList[N + 1];
      indeg = new int[N + 1];
      for (int i = 1; i <= N; i++) {
         g[i] = new ArrayList<>();
      }
      for (int i = 0; i < M; i++) {
         st = new StringTokenizer(br.readLine());
         int x = Integer.parseInt(st.nextToken());
         int y = Integer.parseInt(st.nextToken());
         g[x].add(y);
         indeg[y]++;
      }
   }
}