题目描述

仅供参考

Java 代码

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Arrays;

public class Main {
    static int N = 1010;
    static int M = 10010;
    static int [] e = new int[M];
    static int [] ne = new int[M];
    static int [] h = new int[N];
    static int idx = 0;
    static int n;
    static boolean [][] st = new boolean[N][N];
    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String[] s = br.readLine().split(" ");
        n = Integer.parseInt(s[0]);
        int m = Integer.parseInt(s[1]);
        Arrays.fill(h , -1);
        while(m-- != 0){
            String[] s1 = br.readLine().split(" ");
            int a = Integer.parseInt(s1[0]);
            int b = Integer.parseInt(s1[1]);
            add(a , b);
        }

        for(int i = 1;i<=n;i++){
            dfs(i,i);
        }
        int ans =0;
        for(int i = 1;i<=n;i++){
           if (check(i)){
               ans++;
           }
        }
        System.out.println(ans);
    }


    private static boolean check(int x) {
        for(int i = 1; i<=n;i++){
            if (!st[x][i] && !st[i][x]){
                return false;
            }
        }
        return true;
    }


    private static void dfs(int u, int fa) {
        if (st[fa][u]){
            return;
        }
        st[fa][u] = true;
        for(int i = h[u]; i !=-1 ;i = ne[i]){
            int j = e[i];
            dfs(j,fa);
        }

    }

    private static void add(int a, int b) {
        e[idx] = b;
        ne[idx] = h[a];
        h[a] = idx++;
    }
}