From 7b59476066bab5f5bbd8cad486c15e735a9130b4 Mon Sep 17 00:00:00 2001
From: kim <se6816@naver.com>
Date: Sat, 27 Dec 2025 00:17:23 +0900
Subject: [PATCH 1/2] reverse linked list

---
 reverse-linked-list/se6816.java | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 reverse-linked-list/se6816.java

diff --git a/reverse-linked-list/se6816.java b/reverse-linked-list/se6816.java
new file mode 100644
index 0000000000..4340696f03
--- /dev/null
+++ b/reverse-linked-list/se6816.java
@@ -0,0 +1,22 @@
+/**
+    리스트의 길이 -> N
+    시간 복잡도 : O(N)
+    공간 복잡도 : O(1)
+*/
+class Solution {
+    public ListNode reverseList(ListNode head) {
+        return createReverseHead(head);
+    }
+    private ListNode createReverseHead(ListNode head) {
+        ListNode resultHead = null;
+
+        while (head != null) {
+            ListNode next = head.next; 
+            head.next = resultHead;       
+            resultHead = head;            
+            head = next;     
+        }
+
+        return resultHead;
+    }
+}

From 1ff586cc7e2718a73891cbc2f501eb9333aa17af Mon Sep 17 00:00:00 2001
From: kim <se6816@naver.com>
Date: Sat, 27 Dec 2025 00:20:44 +0900
Subject: [PATCH 2/2] longest-substring-without-repeating-characters

---
 .../se6816.java                               | 37 +++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 longest-substring-without-repeating-characters/se6816.java

diff --git a/longest-substring-without-repeating-characters/se6816.java b/longest-substring-without-repeating-characters/se6816.java
new file mode 100644
index 0000000000..37eb280184
--- /dev/null
+++ b/longest-substring-without-repeating-characters/se6816.java
@@ -0,0 +1,37 @@
+/**
+    투포인터를 이용한 방식
+    문자열 s의 길이 -> N
+    시간 복잡도 : O(N)
+    공간 복잡도 : O(N)
+ */
+
+class Solution {
+    public int lengthOfLongestSubstring(String s) {
+        if(s.length()==0){
+            return 0;
+        }
+        Set<Character> set =new HashSet<>();
+        int start=0;
+        int end=0;
+        int maxSize=0;
+        int len = s.length();
+        while(start < len){
+            
+
+            for(int i=end; i < len;i++){
+                char ch = s.charAt(i);
+                if(set.contains(ch)){
+                    end = i;
+                    break;
+                }
+                set.add(ch);
+            }
+
+            maxSize = Math.max(maxSize, set.size());
+            set.remove(s.charAt(start));
+            start++;
+        
+        }
+        return maxSize;
+    }
+}