added 143.Reorder_List.cpp using cpp , 95.98% faster (#183)

* Create 143.Reorder_List.cpp

* readme

Author: Yashaswinihoney

Diff for: C++/143.Reorder_List.cpp

@@ -0,0 +1,45 @@
+/* medium difficulty */
+
+class Solution {
+public:
+    void reorderList(ListNode* head) {
+
+        //edge cases
+        if ((!head) || (!head->next) || (!head->next->next)) return; 
+
+        int l=0; //to calculate the length
+        ListNode* curr=head;
+        while(curr){
+            l++;
+            curr=curr->next;
+        }
+
+        //stack to store the second half of the elements of the ll
+        stack<ListNode*> s;
+        curr=head;
+
+        //iterating till the end of the first half
+        int m=(l+1)/2;
+        while(m>=1){
+            curr=curr->next;
+            m--;
+        }
+
+        //pushing the second half of the elements in the stack
+        while(curr){
+            s.push(curr);
+            curr=curr->next;
+        }
+
+        //attaching the elements from the top of the stack to the first half of the elements
+        curr=head;
+        while(curr&&!s.empty()){
+            ListNode* temp=s.top();
+            s.pop();
+            temp->next=curr->next;
+            curr->next=temp;
+            curr=curr->next->next;
+        }
+        curr->next=NULL;
+    }
+};

Diff for: README.md

@@ -186,7 +186,9 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 142 | [Linked List Cycle II](https://leetcode.com/problems/linked-list-cycle-ii/)                                           | [Java](./Java/linked-list-cycle-ii.java) <br> [C++](./C++/Linked-List-Cycle-II.cpp) | _O(n)_     | _O(1)_ | Medium     | Slow-Fast Pointers |                                          |
 | 146 | [LRU Cache](https://leetcode.com/problems/lru-cache/)                                                                 | [C++](./C++/LRU-Cache.cpp) <br> [Python](./Python/LRUCache.py)                      | _O(1)_     | _O(k)_ | Medium     | Hash Map           |                                          |
 | 160 | [Intersection of Two Linked Lists](https://leetcode.com/problems/intersection-of-two-linked-lists/)                   | [Java](./Java/intersection-of-two-linked-lists.java)                                | _O(n)_     | _O(1)_ | Easy       | Two Pointers       | [Tutorial](https://youtu.be/uozGB0-gbvI) |
-| 186 | [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/)                                 | [Java](./Java/middle-of-the-linked-list.java)                                       | _O(n)_     | _O(1)_ | Easy       | Two pointers       |                                          |
+| 186 | [Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/)                                 | [Java](./Java/middle-of-the-linked-list.java)                                       | _O(n)_     | _O(1)_ | Easy       | Two pointers       |  
+| 143 | [Reorder List](https://leetcode.com/problems/reorder-list/)                   | [C++](./C++/143.Reorder_List.cpp)                                | _O(n)_     | _O(n)_ | Medium       | Iteration and Stack       |
+                                        |
 
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