解题（DirGraCheckPath--有向图的遍历（深度搜索））

Posted 2021-01-22 hzy1234

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：

 1 package com.yzh.hehe;
 2 
 3 import java.util.ArrayList;
 4 import java.util.Stack;
 5  
 6 
 7 public class DirGraCheckPath {
 8 
 9     public static void main(String[] args) {
10         // TODO Auto-generated method stub
11 
12     }
13     
14      public boolean checkPath(UndirectedGraphNode a, UndirectedGraphNode b) {
15         return  checkSingle(a, b)||checkSingle(b, a);
16      }
17      
18      private boolean checkSingle(UndirectedGraphNode a, UndirectedGraphNode b) {
19          if (a.label==b.label) {
20                 return true;
21             }
22              //深度优先遍历用堆栈实现（广度优先遍历用队列实现）
23             Stack<UndirectedGraphNode> stack= new  Stack<UndirectedGraphNode>();
24             //已遍历的点
25             ArrayList<UndirectedGraphNode> list=new ArrayList<UndirectedGraphNode>();
26             list.add(a);
27             stack.addAll(a.neighbors); 
28             UndirectedGraphNode temp = null;
29             //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）。
30             while (!stack.isEmpty()) {
31                 temp = stack.pop();
32                 if (temp.label==b.label) {
33                     return true;
34                 }
35                 for (UndirectedGraphNode undirectedGraphNode : temp.neighbors) {
36                     if (!stack.contains(undirectedGraphNode)&&!list.contains(undirectedGraphNode)) {
37                         stack.push(undirectedGraphNode);
38                     }
39                 }
40                 list.add(temp);
41             }
42             return false; 
43     }
44 
45 }
46  class UndirectedGraphNode {
47     int label = 0;
48     UndirectedGraphNode left = null;
49     UndirectedGraphNode right = null;
50     ArrayList<UndirectedGraphNode> neighbors = new ArrayList<UndirectedGraphNode>();
51 
52     public UndirectedGraphNode(int label) {
53         this.label = label;
54     }
55 }