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);                     }      }       }