New Problem "Reverse Linked List "

Author: haoel

README.md

@@ -7,6 +7,7 @@ LeetCode
 
 | # | Title | Solution | Difficulty |
 |---| ----- | -------- | ---------- |
+|190|[Reverse Linked List ](https://leetcode.com/problems/reverse-linked-list/)| [C++](./algorithms/reverseLinkedList/reverseLinkedList.cpp)|Easy|
 |189|[Isomorphic Strings](https://leetcode.com/problems/isomorphic-strings/)| [C++](./algorithms/isomorphicStrings/IsomorphicStrings.cpp)|Easy|
 |188|[Count Primes](https://leetcode.com/problems/count-primes/)| [C++](./algorithms/countPrimes/CountPrimes.cpp)|Easy|
 |187|[Remove Linked List Elements](https://leetcode.com/problems/remove-linked-list-elements/)| [C++](./algorithms/removeLinkedListElements/RemoveLinkedListElements.cpp)|Easy|

algorithms/reverseLinkedList/reverseLinkedList.cpp

@@ -0,0 +1,50 @@
+// Source : https://leetcode.com/problems/reverse-linked-list/
+// Author : Hao Chen
+// Date   : 2015-06-09
+
+/********************************************************************************** 
+ * 
+ * Reverse a singly linked list.
+ * 
+ * click to show more hints.
+ * 
+ * Hint:
+ * A linked list can be reversed either iteratively or recursively. Could you implement both?
+ * 
+ *               
+ **********************************************************************************/
+
+
+/**
+ * Definition for singly-linked list.
+ * struct ListNode {
+ *     int val;
+ *     ListNode *next;
+ *     ListNode(int x) : val(x), next(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    ListNode* reverseList_iteratively(ListNode* head) {
+        ListNode *h=NULL, *p=NULL;
+        while (head){
+            p = head->next;
+            head->next = h;
+            h = head;
+            head = p;
+        }
+        return h;
+    }
+    ListNode* reverseList_recursively(ListNode* head) {
+        if (head==NULL || head->next==NULL) return head;
+        ListNode *h = reverseList_recursively(head->next);
+        head->next->next = head;
+        head->next = NULL;
+        return h;
+        
+    }
+    ListNode* reverseList(ListNode* head) {
+        return reverseList_iteratively(head);
+        return reverseList_recursively(head);
+    }
+};