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