add: #224 Merge Two Sorted Lists

Author: sukyoungshin

merge-two-sorted-lists/sukyoungshin.ts

@@ -0,0 +1,39 @@
+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;
+  }
+}
+
+function mergeTwoLists(
+  list1: ListNode | null,
+  list2: ListNode | null
+): ListNode | null {
+  const dummy = new ListNode();
+  let current = dummy;
+
+  const addNode = (val: number) => {
+    current.next = new ListNode(val);
+    current = current.next;
+  };
+
+  while (list1 !== null && list2 !== null) {
+    if (list1.val < list2.val) {
+      addNode(list1.val);
+      list1 = list1.next;
+    } else if (list1.val > list2.val) {
+      addNode(list2.val);
+      list2 = list2.next;
+    } else {
+      addNode(list1.val);
+      addNode(list2.val);
+      list1 = list1.next;
+      list2 = list2.next;
+    }
+  }
+
+  current.next = list1 !== null ? list1 : list2;
+  return dummy.next;
+};