solve: W04 merge two sorted list

Author: eunice-hong

merge-two-sorted-lists/eunice-hong.ts

@@ -0,0 +1,34 @@
+/**
+ * Definition for singly-linked list.
+ * class ListNode {
+ *     val: number
+ *     next: ListNode | null
+ *     constructor(val?: number, next?: ListNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.next = (next===undefined ? null : next)
+ *     }
+ * }
+ */
+/**
+ * 
+ * Time Complexity: O(n + m)
+ * Space Complexity: O(n + m)
+ */
+function mergeTwoLists(list1: ListNode | null, list2: ListNode | null): ListNode | null {
+    if (!list1 && !list2) {
+        // both lists are empty
+        return null
+    } else if (!list1) {
+        // list1 is empty
+        return list2
+    } else if (!list2) {
+        // list2 is empty
+        return list1
+    } else if (list1.val <= list2.val) {
+        // list1's current node is smaller
+        return new ListNode(list1.val, mergeTwoLists(list1.next, list2))
+    } else {
+        // list2's current node is smaller
+        return new ListNode(list2.val, mergeTwoLists(list1, list2.next))
+    }
+};