力扣刷题记录 -- JAVA--30--142. 环形链表 II

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一、题目

二、代码

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution 
{
    public ListNode detectCycle(ListNode head)
    {
        if(head==null) return null;
        if(head.next == null) return null;

        ListNode false_node = new ListNode(0);
        false_node.next =  head;    
        ListNode slow = false_node;
        ListNode fast = false_node;   

        //两层while跳转两次不可取
        while(fast != null)
        {
            fast = fast.next;
             if(fast != null)
             {
                  fast = fast.next;
                  slow = slow.next;
                  if(fast == slow)
                  {
                    System.out.println("进入最终");
                    ListNode new_node1 = false_node;
                    ListNode new_node2 = slow;
                    while(new_node1 != new_node2)
                    {
                        new_node1 = new_node1.next;
                        new_node2 = new_node2.next;
                        System.out.println("寻找");
                    }
                    System.out.println("进入最终且跳出");
                    return new_node1;

                  }
             }
             
        }
        return null;
    }
}

三、运行结果