From 1d6f9b2419269ab63c2635792d67b1ae1073eb91 Mon Sep 17 00:00:00 2001
From: KyungJin Jung <okyungjin@gmail.com>
Date: Sat, 5 Sep 2026 20:15:46 +0900
Subject: [PATCH 1/3] 56. Merge Intervals

---
 merge-intervals/okyungjin.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 merge-intervals/okyungjin.py

diff --git a/merge-intervals/okyungjin.py b/merge-intervals/okyungjin.py
new file mode 100644
index 0000000000..9b93b49ec7
--- /dev/null
+++ b/merge-intervals/okyungjin.py
@@ -0,0 +1,29 @@
+'''
+https://leetcode.com/problems/merge-intervals/description/
+
+N: len(intervals)
+Time: O(N logN), 정렬
+Space: O(N), answer 배열
+'''
+class Solution:
+    def merge(self, intervals: List[List[int]]) -> List[List[int]]:
+        intervals.sort(key=lambda x: x[0])
+
+        answer = [intervals[0]]
+
+        '''
+        [1,4], [5,8] # case A
+        [1,4], [4,7] # case B
+        [1,4], [2,8] # case C
+        '''
+
+        for i in range(1, len(intervals)):
+            curr_start, curr_end = intervals[i]
+            _, last_end = answer[-1]
+
+            if curr_start > last_end: # case A
+                answer.append(intervals[i])
+            elif curr_end > last_end: # case C
+                answer[-1][1] = curr_end
+
+        return answer

From 652d2fcfb1c12b90fd7a954b73e9523b60cef2e5 Mon Sep 17 00:00:00 2001
From: KyungJin Jung <okyungjin@gmail.com>
Date: Sat, 5 Sep 2026 20:38:17 +0900
Subject: [PATCH 2/3] 268. Missing Number

---
 missing-number/okyungjin.py | 43 +++++++++++++++++++++++++++++++++++++
 1 file changed, 43 insertions(+)
 create mode 100644 missing-number/okyungjin.py

diff --git a/missing-number/okyungjin.py b/missing-number/okyungjin.py
new file mode 100644
index 0000000000..70baf8ee80
--- /dev/null
+++ b/missing-number/okyungjin.py
@@ -0,0 +1,43 @@
+'''
+https://leetcode.com/problems/missing-number/description/
+'''
+
+'''
+solution1: 정렬 후 이진탐색
+
+n: len(nums)
+Time: O(n log n), sort
+Space: O(1)
+'''
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        nums.sort() # Time: O(n log n)
+
+        left = 0
+        right = len(nums)
+
+        while left < right: # Time: O(log n)
+            mid = (left + right) // 2
+
+            if nums[mid] > mid:
+                right = mid
+            else:
+                left = mid + 1
+
+        return left
+
+'''
+solution2: 0부터 n까지 더한 값에서 배열의 전체 합을 빼기
+
+n: len(nums)
+Time: O(n)
+Space: O(1)
+'''
+class Solution:
+    def missingNumber(self, nums: List[int]) -> int:
+        n = len(nums)
+
+        complete_sum = n * (n + 1) // 2
+        actual_sum = sum(nums) # Time: O(n)
+
+        return complete_sum - actual_sum

From 5cd158fde4fd7742934418092fa7f2b8e8f07c25 Mon Sep 17 00:00:00 2001
From: KyungJin Jung <okyungjin@gmail.com>
Date: Sat, 5 Sep 2026 21:25:51 +0900
Subject: [PATCH 3/3] 143. Reorder List

---
 reorder-list/okyungjin.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 reorder-list/okyungjin.py

diff --git a/reorder-list/okyungjin.py b/reorder-list/okyungjin.py
new file mode 100644
index 0000000000..35dbd2c164
--- /dev/null
+++ b/reorder-list/okyungjin.py
@@ -0,0 +1,29 @@
+"""
+https://leetcode.com/problems/reorder-list/
+
+N: number of nodes
+Time: O(N)
+Space: O(N)
+"""
+class Solution:
+    def reorderList(self, head: Optional[ListNode]) -> None:
+        nodes = []
+        curr = head
+        while curr:
+            nodes.append(curr)
+            curr = curr.next
+        
+        left = 0
+        right = len(nodes) - 1
+        
+        while left < right:
+            nodes[left].next = nodes[right]
+            left += 1
+
+            if left == right:
+                break
+                
+            nodes[right].next = nodes[left]
+            right -= 1
+            
+        nodes[left].next = None