题解 | #链表中环的入口结点#

/*
public class ListNode
{
    public int val;
    public ListNode next;
    public ListNode (int x)
    {
        val = x;
    }
}*/
class Solution {
    public ListNode EntryNodeOfLoop(ListNode pHead) {
        // write code here
        if (pHead == null) return null;
        ListNode fast, slow;
        fast = slow = pHead;
        while (fast != null && fast.next != null) {
            fast = fast.next.next;
            slow = slow.next;
            if (fast == slow) { //有环要进行的处理,找出环的入口结点
                fast = pHead;
                while (fast != slow) {
                    fast = fast.next;
                    slow = slow.next;
                }
                return  slow;
            }
        }
        return null;
    }
}