剑指offer-链表中环的入口结点

 1 /*
 2  public class ListNode {
 3     int val;
 4     ListNode next = null;
 5 
 6     ListNode(int val) {
 7         this.val = val;
 8     }
 9 }
10 */
11 import java.util.HashMap;
12 import java.util.Map;
13 public class Solution {
14 
15     public ListNode EntryNodeOfLoop(ListNode pHead)
16     {
17              Map<ListNode,Integer>map=new HashMap<ListNode,Integer>();
18        while(pHead!=null){
19            if(map.containsKey(pHead)){
20                return pHead;
21            }else{
22                map.put(pHead,1);
23            }
24            pHead=pHead.next;
25        }
26        return null;
27     }
28 }