Update 21. Merge Two Sorted Lists.md

Author: developer-mohitsoni

Linked List Problem/21. Merge Two Sorted Lists.md

@@ -40,15 +40,62 @@ Return <i>the head of the merged linked list.</i>
 ```cpp
 class Solution {
 public:
-    void deleteNode(ListNode* node) {
+    ListNode* mergeTwoLists(ListNode* list1, ListNode* list2) {
 
-        ListNode *nextNode = node->next;
+        ListNode *merge, *tail;
 
-        swap(nextNode->val, node->val);
+        if(list1 == NULL)
+        {
+            return list2;
+        }
+        if(list2 == NULL)
+        {
+            return list1;
+        }
 
-        node->next = nextNode->next;
+        if(list1->val < list2->val)
+        {
+            merge = list1;
+            
+            list1 = list1->next;
+        }
+        else
+        {
+            merge = list2;
+            
+            list2 = list2->next;
+        }
 
-        delete(nextNode);
+        tail = merge;
+        
+        while(list1 != NULL && list2 != NULL)
+        {
+            if(list1->val < list2->val)
+            {
+                tail->next = list1;
+                
+                list1 = list1->next;
+                
+                tail = tail->next;
+            }
+            else
+            {
+                tail->next = list2;
+                
+                list2 = list2->next;
+                
+                tail = tail->next;
+            }
+        }
+        if(list1 != NULL)
+        {
+            tail->next = list1;
+        }
+        if(list2 != NULL)
+        {
+            tail->next = list2;
+        }
+        return merge;
     }
 };
 ```