hdu 1269 迷宫城堡 java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
import java.util.Stack;
class Main {  
    private int numOfNode;  
    private List< ArrayList<Integer> > graph;//图  
    private List< ArrayList<Integer> > result;//保存极大强连通图  
    private boolean[] inStack; 
    private Stack<Integer> stack;  
    private int[] dfn;  
    private int[] low;  
    private int time;
      public static void main(String[] args) {
        Scanner in = new Scanner(System.in 
);
        while(in.hasNext()){
            int n=in.nextInt();
            int m=in.nextInt();
            if(n==0&&m==0){
                break;
            }
            List< ArrayList<Integer> > graph = new ArrayList<ArrayList<Integer>>();  
            for(int i=0;i<n;i++){                
                graph.add(new ArrayList<Integer>());  
            }
            for(int i=0;i<m;i++){
                int a=in.nextInt()-1;
                int b=in.nextInt()-1;
                graph.get(a).add(b);
            }
            Main t = new Main(graph, n);  
            List< ArrayList<Integer> > result = t.run();  
                    //打印结果  
            int sum=0;
            for(int i=0;i<result.size();i++){
                if(sum<result.get(i).size()){
                    sum=result.get(i).size();  
                  
                }  
                  
            }  if(sum==n){
                System.out.println("Yes");
            }else{
                System.out.println("No");
            }
        }

            
    }
    public Main(List< ArrayList<Integer> > graph,int numOfNode){  
        this.graph = graph;  
        this.numOfNode = numOfNode;  
        this.inStack = new boolean[numOfNode];  
        this.stack = new Stack<Integer>();  
        dfn = new int[numOfNode];  
        low = new int[numOfNode];  
        Arrays.fill(dfn, -1);//将dfn所有元素都置为-1，其中dfn[i]=-1代表i还有没被访问过。  
        Arrays.fill(low, -1);  
        result = new ArrayList<ArrayList<Integer>>();  
    }  
      
    public List< ArrayList<Integer> > run(){  
        for(int i=0;i<numOfNode;i++){  
            if(dfn[i]==-1){  
                tarjan(i);  
            }  
        }  
        return result;  
    }  
    public void tarjan(int current){  
        dfn[current]=low[current]=time++;  
        inStack[current]=true;  
        stack.push(current);  
          
        for(int i=0;i<graph.get(current).size();i++){  
            int next = graph.get(current).get(i);  
            if(dfn[next]==-1){
                tarjan(next);  
                low[current]=Math.min(low[current], low[next]);  
            }else if(inStack[next]){  
                low[current]=Math.min(low[current], dfn[next]);  
            }  
        }  
        if(low[current]==dfn[current]){  
            ArrayList<Integer> temp =new ArrayList<Integer>();  
            int j = -1;  
            while(current!=j){  
                j = stack.pop();  
                inStack[j]=false;  
                temp.add(j);  
            }  
            result.add(temp);             
        }  
    }       
}