Update 23. 链表中环的入口结点.md

题目链接改为力扣中的对应题目，题目描述和代码按该题的接口调整。

notes/23. 链表中环的入口结点.md

@@ -1,6 +1,6 @@
 # 23. 链表中环的入口结点
 
-[NowCoder](https://www.nowcoder.com/practice/253d2c59ec3e4bc68da16833f79a38e4?tpId=13&tqId=11208&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
+[Leetcode](https://leetcode.cn/problems/linked-list-cycle-ii/)
 
 ## 题目描述
 
@@ -25,19 +25,22 @@
 <div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/bb7fc182-98c2-4860-8ea3-630e27a5f29f.png" width="500"/> </div><br>
 
 ```java
-public ListNode EntryNodeOfLoop(ListNode pHead) {
-    if (pHead == null || pHead.next == null)
+public ListNode detectCycle(ListNode head) {
+    if (head == null || head.next == null)
         return null;
-    ListNode slow = pHead, fast = pHead;
-    do {
+    ListNode slow = head, fast = head;
+    while (fast != null && fast.next != null) {
+        slow = slow.next;
         fast = fast.next.next;
-        slow = slow.next;
-    } while (slow != fast);
-    fast = pHead;
-    while (slow != fast) {
-        slow = slow.next;
-        fast = fast.next;
+        if (slow == fast) {
+            fast = head;
+            while (slow != fast) {
+                slow = slow.next;
+                fast = fast.next;
+            }
+            return slow;
+        }
     }
-    return slow;
+    return null;
 }
 ```