Poj Solution 3660

http://poj.org/problem?id=3660

//* @author popop0p0popo
import java.util.*;
import java.io.*;

public class Main{
 public static void main(String[] args){
  Scanner in=new Scanner(new BufferedReader(new InputStreamReader(System.in)));
        int n=in.nextInt();
        int m=in.nextInt();
        int[][] p=new int[n][n];
        for (int i=0;i< n ;i++ ){
            for (int j=0;j< n ;j++ ){
                p[i][j]=101;
            }
            p[i][i]=0;
        }
        for (int i=0;i< m ;i++ ){
            p[in.nextInt()-1][in.nextInt()-1]=1;
        }
        for (int k=0;k< n ;k++ ){
            for (int i=0;i< n ;i++ ){
                for (int j=0;j< n ;j++ ){
                 p[i][j]=getMin(p[i][j],p[i][k]+p[k][j]);
                }
            }
        }
        int w=0;
        for (int i=0;i< n ;i++ ){
            int t=0;
            for (int j=0;j< n ;j++ ){
                if (p[i][j]< 101||p[j][i]< 101){
                    t++;
                }
            }
            if (t==n){
                w++;
            }
        }
        System.out.println(w);
    }

    public static int getMin(int a,int b){
        if (a>=b){
            return b;
        }
        else{
            return a;
        }
    }
}