解题（DirGraCheckPath--有向图的遍历（深度搜索））

题目描述

对于一个有向图，请实现一个算法，找出两点之间是否存在一条路径。

给定图中的两个结点的指针DirectedGraphNode* a, DirectedGraphNode* b(请不要在意数据类型，图是有向图),请返回一个bool，代表两点之间是否存在一条路径(a到b或b到a)。

代码如下：

 package com.yzh.hehe;

 import java.util.ArrayList;
 import java.util.Stack;

 public class DirGraCheckPath {

     public static void main(String[] args) {
         // TODO Auto-generated method stub

     }

      public boolean checkPath(UndirectedGraphNode a, UndirectedGraphNode b) {
         return  checkSingle(a, b)||checkSingle(b, a);
      }

      private boolean checkSingle(UndirectedGraphNode a, UndirectedGraphNode b) {
          if (a.label==b.label) {
                 return true;
             }
              //深度优先遍历用堆栈实现（广度优先遍历用队列实现）
             Stack<UndirectedGraphNode> stack= new  Stack<UndirectedGraphNode>();
             //已遍历的点
             ArrayList<UndirectedGraphNode> list=new ArrayList<UndirectedGraphNode>();
             list.add(a);
             stack.addAll(a.neighbors);
             UndirectedGraphNode temp = null;
             //深度遍历一个点，看是否目标点，是结束，否则再将此点的连接点放入栈中等待遍历重复（入栈将连接点中已经在栈中和已遍历过的点去掉）。
             while (!stack.isEmpty()) {
                 temp = stack.pop();
                 if (temp.label==b.label) {
                     return true;
                 }
                 for (UndirectedGraphNode undirectedGraphNode : temp.neighbors) {
                     if (!stack.contains(undirectedGraphNode)&&!list.contains(undirectedGraphNode)) {
                         stack.push(undirectedGraphNode);
                     }
                 }
                 list.add(temp);
             }
             return false;
     }

 }
  class UndirectedGraphNode {
     int label = 0;
     UndirectedGraphNode left = null;
     UndirectedGraphNode right = null;
     ArrayList<UndirectedGraphNode> neighbors = new ArrayList<UndirectedGraphNode>();

     public UndirectedGraphNode(int label) {
         this.label = label;
     }
 }