Updated mergeList.cpp

Lecture049 Linked List Day6/mergeList.cpp

@@ -22,50 +22,61 @@
 
 ************************************************************/
 
-void solve(Node<int>* first, Node<int>* second) {
-
-
-    Node* curr1 = first;
-    Node* next1 = curr1 -> next;
-
-    Node* curr2 = second;
-    Node* next2 = curr2 -> next;
-
-    while(next1 != NULL && curr2 != NULL) {
-
-        if( (curr2 -> data >= curr1 -> data ) 
-           && ( curr2 -> data <= next1 -> data)) {
-
+Node<int>* solve(Node<int>* first, Node<int>* second) {
+
+    //if only one element is present in first list
+    if(first -> next == NULL) {
+        first -> next = second;
+        return first;
+    }
+
+    Node<int>* curr1 = first;
+    Node<int>* next1 = curr1 -> next;
+
+    Node<int>* curr2 = second;
+    Node<int>* next2 = curr2 -> next;
+
+    while(next1 != NULL && curr2 !=NULL) {
+
+        if((curr2 -> data >= curr1 -> data)  
+            && ( curr2 -> data <= next1 -> data)) {
+
+            //add node in between the first list
             curr1 -> next = curr2;
+            next2 = curr2 -> next;
             curr2 -> next = next1;
+            //update pointers
+
             curr1 = curr2;
             curr2 = next2;
         }
-        else {
-
+        else{
+            //go one step ahead in first list
+            curr1 = next1;
+            next1 = next1 -> next;
+
+            if(next1 == NULL) {
+                curr1 -> next = curr2;
+                return first;
+            }
         }
-
-
     }
-
-
+    return first;
 }
 
 Node<int>* sortTwoLists(Node<int>* first, Node<int>* second)
 {
-    if(first == NULL)
+    if(first == NULL) 
         return second;
-    
+
     if(second == NULL)
         return first;
-    
-    if(first -> data <= second -> data ){
-        solve(first, second);
+
+    if(first -> data <= second -> data) {
+        return solve(first, second);
     }
     else
     {
-        solve(second, first);
+        return solve(second, first);
     }
-
-
 }