Java实现 洛谷 P3916 图的遍历（反向DFS+记忆化搜索）

P3916 图的遍历

输入输出样例
输入
4 3
1 2
2 4
4 3
输出
4 4 3 4

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
import java.util.Vector;

public class 图的遍历 {
	static Vector<Vector<Integer>> vec = new Vector<Vector<Integer>>();
	static int[] num;

	public static void main(String[] args) throws IOException {
		StreamTokenizer st = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));

        st.nextToken();
        int V = (int) st.nval; 

        st.nextToken();
        int E = (int) st.nval;
        for (int i = 0; i <= V; i ++) {
			 vec.add(new Vector<Integer>());
		}

        int head,tail;
        for(int i=0;i<E;i++)
        {
        	st.nextToken();
        	head = (int) st.nval;
            st.nextToken();
            tail = (int) st.nval;
            vec.get(tail).add(head);
        }

		num = new int[V + 1];

		for (int i = V; i >=1; i--) {
			dfs(i,i);
		}
		for (int i = 1; i<=V; i++) {
			System.out.print(num[i]+" ");
		}
	}

	public static void dfs(int start,int end) {
		if(num[start]!=0) {

			return ;
		}
		num[start]=end;
		int res = 0;
		for (int node : vec.get(start)) {
				  dfs(node,end );
		}
	}
}