Create 206_Reverse Linked List.cpp

Author: CY-Gu

Diff for: 206_Reverse Linked List.cpp

@@ -0,0 +1,35 @@
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode() : val(0), next(nullptr) {}
+ *     ListNode(int x) : val(x), next(nullptr) {}
+ *     ListNode(int x, ListNode *next) : val(x), next(next) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* reverseList(ListNode* head) {
+        
+        if(!head)
+            return NULL;
+        
+        ListNode *before = NULL;
+        ListNode *current = head;
+        ListNode *after = head->next;
+
+        while(after){
+            
+            current->next = before;
+            before = current;
+            current = after;
+            after = after->next;
+        }
+        //最後一個current還指著null，要將它指回前一個
+        current->next = before; 
+        
+        return current;
+        
+    }
+};