找出有环链表的第一个起始点

客官°小女子只卖身不卖艺 2022-05-23 04:42 147阅读 0赞

![这里写图片描述][70]

class ListNode {
         int val;
          ListNode next;
          ListNode(int x) {
              val = x;
              next = null;
          }
      }
    
    public class Solution {
        //找出有环链表的第一个起始点
        public ListNode detectCycle(ListNode head) {
            if(head==null||head.next==null||head.next.next==null)
                return null;   
            ListNode slow=head.next;
            ListNode fast=head.next.next;
             while (fast!=slow&&fast!=null&&fast.next!=null) {
                 fast=fast.next.next;
                 slow=slow.next;
             }
             if(fast==null||fast.next==null)
             {
                return null;
             }else{
    
                fast=head;
                while(fast!=slow)
                {
                     fast=fast.next;
                     slow=slow.next;
                }
             }
             return slow;
        }
    
        public static void main(String[]args){
            //System.out.println("Hello");
            ListNode head=new ListNode(1);
            head.next=new ListNode(2);
            head.next.next=new ListNode(3);
            ListNode tmp=new ListNode(4);
            head.next.next.next=tmp;
            tmp.next=head.next;
            Solution s=new Solution();
            System.out.println(s.detectCycle(head).val);
        }
    }

[70]: /images/20220523/cc35814277794234a6143545440f63b4.png