题解 | #链表中环的入口结点#做题及学习积累

import java.util.*;
/*
 public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}
*/
public class Solution {

    public ListNode EntryNodeOfLoop(ListNode pHead) {
        if(pHead == null){
            return null;
        }
        ListNode fast = pHead;
        ListNode slow = pHead;

        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 = pHead;
        while(fast != slow){
            fast = fast.next;
            slow = slow.next;
        }
        return fast;
    }
}

还好有印象是快慢指针，但是最后如何获取头结点还需要推理