leetcode new problems

leetcode/lc21/MergeLists.cpp

@@ -0,0 +1,36 @@
+/**
+ * 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* mergeTwoLists(ListNode* l1, ListNode* l2) {
+        ListNode* dummy = new ListNode(0);
+        ListNode* cur = dummy;
+
+        while(l1 && l2){
+            if((l1->val) < (l2->val) ){
+                cur->next = l1;
+                l1 = l1->next;
+            }
+            else{
+                cur->next = l2;
+                l2 = l2->next;
+            }
+            cur = cur->next;
+        }
+        cur->next = l1? l1 : l2;
+        ListNode* head = dummy->next;
+        delete dummy;
+        return head;
+
+    }
+};
+// TC : O(m+n)
+// SC : O(1)