week4: merge-two-sorted-lists

Author: reeseo3o

merge-two-sorted-lists/reeseo3o.js

@@ -0,0 +1,42 @@
+/**
+ * 1. Recursive approach
+ * Time complexity: O(n + m)
+ * Space complexity: O(n + m)
+ */
+// const mergeTwoLists = (list1, list2) => {
+//     if (!list1) return list2;
+//     if (!list2) return list1;
+//
+//     if (list1.val <= list2.val) {
+//         list1.next = mergeTwoLists(list1.next, list2);
+//         return list1;
+//     } else {
+//         list2.next = mergeTwoLists(list1, list2.next);
+//         return list2;
+//     }
+// };
+
+/**
+ * 2. Iterative approach + Dummy Node
+ * Time complexity: O(n + m)
+ * Space complexity: O(1)
+ */
+const mergeTwoLists = (list1, list2) => {
+    const dummy = new ListNode(-1);
+    let current = dummy;
+
+    while (list1 !== null && list2 !== null) {
+        if (list1.val <= list2.val) {
+            current.next = list1;
+            list1 = list1.next;
+        } else {
+            current.next = list2;
+            list2 = list2.next;
+        }
+        current = current.next;
+    }
+
+    current.next = list1 ?? list2;
+
+    return dummy.next;
+};