2026-02-21 문제 풀었어요

Leetcode/Easy/21_merge-two-sorted-lists.ts

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+/**
+ * ⭐️ 문제 정보 ⭐️
+ * 문제 : 21 - Merge Two Sorted Lists
+ * 레벨 : Easy
+ * 링크 : https://leetcode.com/problems/merge-two-sorted-lists
+ */
+
+// ANCHOR 2026.02.21 풀이
+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 cur = dummy;
+  let ptr1 = list1;
+  let ptr2 = list2;
+
+  while (ptr1 && ptr2) {
+    if (ptr1.val < ptr2.val) {
+      // cur.next = new ListNode(ptr1.val);
+      cur.next = ptr1; // 기존 노드를 재사용하여 메모리 효율성 향상
+      ptr1 = ptr1.next;
+    } else {
+      // cur.next = new ListNode(ptr2.val);
+      cur.next = ptr2;
+      ptr2 = ptr2.next;
+    }
+    cur = cur.next;
+  }
+
+  while (ptr1) {
+    // cur.next = new ListNode(ptr1.val);
+    cur.next = ptr1;
+    ptr1 = ptr1.next;
+    cur = cur.next;
+  }
+  while (ptr2) {
+    // cur.next = new ListNode(ptr2.val);
+    cur.next = ptr2;
+    ptr2 = ptr2.next;
+    cur = cur.next;
+  }
+
+  return dummy.next;
+}