题解 | #链表中环的入口结点#

/*
 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 || pHead.next == null){
            return null;
        }

        ListNode slow = pHead, fast = pHead, ano = pHead;
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
            if(fast == slow){
                //相遇，表示有环。这时候，慢的和ano每次走一步，相遇即环的入口
                while(ano != slow){
                    slow = slow.next;
                    ano = ano.next;
                }

                return ano;
            }
        }

        return null;
    }
}