題目描述

對於一個有向圖，請實現一個演算法，找出兩點之間是否存在一條路徑。

給定圖中的兩個結點的指標DirectedGraphNode* a, DirectedGraphNode* b(請不要在意資料型別，圖是有向圖),請返回一個bool，代表兩點之間是否存在一條路徑(a到b或b到a)。

 程式碼如下：

 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              //深度優先遍歷用堆疊實現（廣度優先遍歷用佇列實現）
23             Stack<UndirectedGraphNode> stack= new  Stack<UndirectedGraphNode>();
24             //
 
已遍歷的點
25             ArrayList<UndirectedGraphNode> list=new ArrayList<UndirectedGraphNode>();
26             list.add(a);
27             stack.addAll(a.neighbors); 
28             UndirectedGraphNode temp = null;
29             //深度遍歷一個點，看是否目標點，是結束，否則再將此點的連線點放入棧中等待遍歷重複（入棧將連線點中已經在棧中和已遍歷過的點去掉）。
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 }