From 49ba24125d9189654cc18ccb456df2039d89df89 Mon Sep 17 00:00:00 2001
From: Suhyen Im <suhyenim.kor@gmail.com>
Date: Sat, 16 Aug 2025 23:57:23 +0900
Subject: [PATCH] suhyenim] WEEK04 solutions

---
 merge-two-sorted-lists/suhyenim.java | 83 ++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 merge-two-sorted-lists/suhyenim.java

diff --git a/merge-two-sorted-lists/suhyenim.java b/merge-two-sorted-lists/suhyenim.java
new file mode 100644
index 000000000..2daf9fd44
--- /dev/null
+++ b/merge-two-sorted-lists/suhyenim.java
@@ -0,0 +1,83 @@
+/* [5th/week04] 21. Merge Two Sorted Lists
+
+1. 문제 요약
+링크: https://leetcode.com/problems/merge-two-sorted-lists/description/
+두 개의 정렬된 리스트를 오름차순으로 병합한 리스트를 반환
+
+2. 문제 풀이
+풀이1: 두 리스트의 head 비교해서 더 작은 값 선택 -> 한쪽이 null되면 재귀를 통해 이어붙여서 마무리
+성공/실패: 시간 복잡도는 O(m+n), 공간 복잡도는 O(m+n) 
+=> Time: 0 ms (100%), Space: 43 MB (8.18%)
+
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        if (l1 == null || l2 == null)
+            return l1 != null ? l1 : l2;
+        if (l1.val < l2.val) {
+            l1.next = mergeTwoLists(l1.next, l2);
+            return l1;
+        } else {
+            l2.next = mergeTwoLists(l1, l2.next);
+            return l2;
+        }
+    }
+}
+
+풀이2: 두 리스트의 head 비교해서 더 작은 값 선택해서 node.next에 연결 -> 한쪽이 null되면 dummy.next 반환
+성공/실패: 시간 복잡도는 O(m+n), 공간 복잡도는 O(1) 
+=> Time: 0 ms (100%), Space: 43.2 MB (8.18%)
+
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        ListNode dummy = new ListNode(-1); 
+        ListNode node = dummy; 
+
+        while (l1 != null && l2 != null) {
+            if (l1.val < l2.val) {
+                node.next = l1;
+                l1 = l1.next;
+            } else {
+                node.next = l2;
+                l2 = l2.next;
+            }
+            node = node.next;
+        }
+
+        node.next = l1 != null ? l1 : l2;
+        return dummy.next;
+    }
+}
+
+*/
+
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+
+class Solution {
+    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
+        ListNode dummy = new ListNode(-1); 
+        ListNode node = dummy;
+
+        while (l1 != null && l2 != null) {
+            if (l1.val < l2.val) {
+                node.next = l1;
+                l1 = l1.next;
+            } else {
+                node.next = l2;
+                l2 = l2.next;
+            }
+            node = node.next;
+        }
+
+        node.next = l1 != null ? l1 : l2;
+        return dummy.next;
+    }
+}