leetcode new problems

leetcode/lc21/RecursiveMerge.cpp

@@ -0,0 +1,17 @@
+class Solution{
+    public : 
+        ListNode* mergeTwoLists(ListNode* l1, ListNode* l2){
+            if(!l1 || !l2)
+                return l1? l1: l2;
+            if(l1->val > l2->val)
+                swap(l1,l2);
+            l1->next = mergeTwoLists(l1->next, l2);
+            return l1;
+
+        }
+}
+
+//At every step, pick the smaller head node, attach it to the result,and recursively merge the remaining lists
+//TC : O(m+n)
+//SC: O(m+n), recursion stack space
+