链表专题更新cpp代码

animation-simulation/链表篇/leetcode142环形链表2.md

@@ -123,7 +123,9 @@ public class Solution {
 
 ![环形链表2](https://cdn.jsdelivr.net/gh/tan45du/photobed@master/photo/环形链表2.elwu1pw2lw0.gif)
 
+**题目代码**
 
+Java Code:
 
 ```java
 public class Solution {
@@ -153,3 +155,34 @@ public class Solution {
 }
 ```
 
+C++ Code:
+
+```cpp
+class Solution {
+public:
+    ListNode *detectCycle(ListNode *head) {
+        //快慢指针
+        ListNode * fast = head;
+        ListNode * low  = head;
+        //设置循环条件
+        while (fast != nullptr && fast->next != nullptr) {
+            fast = fast->next->next;
+            low = low->next;
+            //相遇
+            if (fast == low) {
+                //设置一个新的指针，从头节点出发，慢指针速度为1，所以可以使用慢指针从相遇点出发
+                ListNode * newnode = head;
+                while (newnode != low) {        
+                    low = low->next;
+                    newnode = newnode->next;
+                }
+                //在环入口相遇
+                return low;
+            }
+        } 
+        return nullptr;
+        
+    }
+};
+```
+