From 0169df984e7e8cfd1d1b056cd7e0282781b26d6d Mon Sep 17 00:00:00 2001
From: KyungJin Jung <okyungjin@gmail.com>
Date: Wed, 5 Aug 2026 00:59:45 +0900
Subject: [PATCH 1/2] 206. Reverse Linked List

---
 reverse-linked-list/okyungjin.py | 50 ++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100644 reverse-linked-list/okyungjin.py

diff --git a/reverse-linked-list/okyungjin.py b/reverse-linked-list/okyungjin.py
new file mode 100644
index 0000000000..50bf87b3e6
--- /dev/null
+++ b/reverse-linked-list/okyungjin.py
@@ -0,0 +1,50 @@
+# https://leetcode.com/problems/reverse-linked-list/
+
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+
+"""
+Time: O(N)
+Space O(N)
+"""
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if not head:
+            return None
+            
+        stack = []
+
+        while head:
+            stack.append(head)
+            head = head.next
+
+        dummy_head = ListNode()
+        curr = dummy_head
+        
+        while stack:
+            curr.next = stack.pop()
+            curr = curr.next
+
+        curr.next = None
+
+        return dummy_head.next
+
+
+"""
+Time: O(N)
+Space O(1)
+"""
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev = None
+        curr = head
+
+        while curr:
+            temp = curr.next
+            curr.next = prev
+            prev, curr = curr, temp
+
+        return prev

From 1b4efaaa4dccf0790182fe1af615dff3f49aa227 Mon Sep 17 00:00:00 2001
From: KyungJin Jung <okyungjin@gmail.com>
Date: Sat, 8 Aug 2026 17:50:26 +0900
Subject: [PATCH 2/2] 3. Longest Substring Without Repeating Characters

---
 .../okyungjin.py                              | 24 +++++++++++++++++++
 1 file changed, 24 insertions(+)
 create mode 100644 longest-substring-without-repeating-characters/okyungjin.py

diff --git a/longest-substring-without-repeating-characters/okyungjin.py b/longest-substring-without-repeating-characters/okyungjin.py
new file mode 100644
index 0000000000..9ec4769df0
--- /dev/null
+++ b/longest-substring-without-repeating-characters/okyungjin.py
@@ -0,0 +1,24 @@
+"""
+N: `s`의 길이, M: `s`에서 중복을 제외한 문자의 개수
+Time: O(N)
+Space: O(min(N,M))
+"""
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+         # 문자의 최근 인덱스를 저장
+        char_map = {}
+
+        left = 0
+        max_len = 0
+
+        for right, char in enumerate(s):
+            if char in char_map and char_map[char] >= left:
+                left = char_map[char] + 1
+
+            char_map[char] = right
+            
+            curr_len = right - left + 1
+            if curr_len > max_len:
+                max_len = curr_len
+
+        return max_len