Leetcode题解 142. Linked List Cycle II

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.

《程序员面试金典》原题

/** * 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(null==head) return null;        ListNode fast=head;        ListNode slow=head;        while(fast!=null&&fast.next!=null){            fast=fast.next.next;            slow=slow.next;            if(fast==slow){                break;            }        }        if(fast==null||fast.next==null){            return null;        }        fast=head;        while(fast!=slow){            fast=fast.next;            slow=slow.next;        }        return slow;    }}