Merge pull request doocs#44 from KongJHong/master

Add solution 142[CPP]

Author: yanglbme

solution/142.Linked List Cycle II/README.md

@@ -67,4 +67,32 @@ public class Solution {
 
     }
 }
+```
+
+#### CPP
+
+```C++
+class Solution {
+public:
+    ListNode *detectCycle(ListNode *head) {
+        if(head == NULL)return NULL;
+        ListNode *fast = head;
+        ListNode *slow = head;
+        while(fast != NULL && fast->next != NULL){
+            fast = fast->next->next;
+            slow = slow->next;
+            
+            if(fast == slow){
+                slow = head;
+                while(slow != fast){
+                    fast = fast->next;
+                    slow = slow->next;
+                }
+                return fast;
+            }
+        }
+        return NULL;//无环
+    }
+};
+
 ```

solution/142.Linked List Cycle II/Solution.cpp

@@ -0,0 +1,22 @@
+class Solution {
+public:
+    ListNode *detectCycle(ListNode *head) {
+        if(head == NULL)return NULL;
+        ListNode *fast = head;
+        ListNode *slow = head;
+        while(fast != NULL && fast->next != NULL){
+            fast = fast->next->next;
+            slow = slow->next;
+            
+            if(fast == slow){
+                slow = head;
+                while(slow != fast){
+                    fast = fast->next;
+                    slow = slow->next;
+                }
+                return fast;
+            }
+        }
+        return NULL;//无环
+    }
+};