题目：图中两个点之间的路线

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给出一张有向图，设计一个算法判断两个点 s 与 t 之间是否存在路线。

您在真实的面试中是否遇到过这个题？

Yes

样例

如下图:
A----->B----->C
\     |
\    |
   \   |
    \ v
     ->D----->E

for s = B and t = E, return true

for s = D and t = C, return false
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解题思路：

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/*** Definition for Directed graph.* class DirectedGraphNode {*     int label;*     ArrayList<DirectedGraphNode> neighbors;*     DirectedGraphNode(int x) {*         label = x;*         neighbors = new ArrayList<DirectedGraphNode>();*     }* };*/public class Solution {   /**     * @param graph: A list of Directed graph node     * @param s: the starting Directed graph node     * @param t: the terminal Directed graph node     * @return: a boolean value     */    public boolean hasRoute(ArrayList<DirectedGraphNode> graph,                             DirectedGraphNode s, DirectedGraphNode t) {        // write your code here          if(0==graph.size()||null==graph) return false;          Queue<DirectedGraphNode> curNodes = new LinkedList<DirectedGraphNode>();          curNodes.add(s);          while(null!=curNodes&&curNodes.size()>0){                    DirectedGraphNode curNode = curNodes.poll();                    if(curNode!=null){                         if(curNode==t){                              return true;                         }else {                              ArrayList<DirectedGraphNode> neighbors = curNode.neighbors;                              for(DirectedGraphNode node:neighbors){                                        curNodes.add(node);                                   }                              }                         }                                             }          return false;    }}

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