From 4836151a04615e19e30bc88bca1deb359467b662 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 22:50:15 +0900
Subject: [PATCH 01/26] contains duplicate solution

---
 contains-duplicate/yuseok89.py | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 contains-duplicate/yuseok89.py

diff --git a/contains-duplicate/yuseok89.py b/contains-duplicate/yuseok89.py
new file mode 100644
index 0000000000..8648095834
--- /dev/null
+++ b/contains-duplicate/yuseok89.py
@@ -0,0 +1,11 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        dup_check = set()
+
+        for num in nums:
+            if num in dup_check:
+                return True
+
+            dup_check.add(num)
+
+        return False

From cdc00da1eda0b122b45a94b8800d06edb786024b Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 22:51:51 +0900
Subject: [PATCH 02/26] two sum solution

---
 two-sum/yuseok89.py | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
 create mode 100644 two-sum/yuseok89.py

diff --git a/two-sum/yuseok89.py b/two-sum/yuseok89.py
new file mode 100644
index 0000000000..2033711307
--- /dev/null
+++ b/two-sum/yuseok89.py
@@ -0,0 +1,14 @@
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        idx_map = {}
+
+        for idx, num in enumerate(nums):
+            idx_map[num] = idx
+
+        for idx, num in enumerate(nums):
+            need = target - num
+
+            if need in idx_map and idx != idx_map[need]:
+                return [idx, idx_map[need]]
+
+        return []

From cc0a988332934a6eb50e471feac5e726b5fd7cd6 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 22:54:01 +0900
Subject: [PATCH 03/26] top k frequent elements solution

---
 top-k-frequent-elements/yuseok89.py | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)
 create mode 100644 top-k-frequent-elements/yuseok89.py

diff --git a/top-k-frequent-elements/yuseok89.py b/top-k-frequent-elements/yuseok89.py
new file mode 100644
index 0000000000..bfaa5de681
--- /dev/null
+++ b/top-k-frequent-elements/yuseok89.py
@@ -0,0 +1,28 @@
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+
+        import heapq
+
+        heap = []
+        cnt = {}
+
+        for num in nums:
+            if num not in cnt:
+                cnt[num] = 0
+
+            cnt[num] = cnt[num] + 1
+
+        for num in cnt.keys():
+            if len(heap) < k:
+                heapq.heappush(heap, cnt[num])
+            elif heap[0] < cnt[num]:
+                heapq.heappop(heap)
+                heapq.heappush(heap, cnt[num])
+
+        ret = []
+
+        for num in cnt.keys():
+            if cnt[num] >= heap[0]:
+                ret.append(num)
+
+        return ret

From c894055dfd11492cecaff47fcc0a2e3c2ce6faf4 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 22:55:18 +0900
Subject: [PATCH 04/26] longest consecutive sequence solution

---
 longest-consecutive-sequence/yuseok89.py | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)
 create mode 100644 longest-consecutive-sequence/yuseok89.py

diff --git a/longest-consecutive-sequence/yuseok89.py b/longest-consecutive-sequence/yuseok89.py
new file mode 100644
index 0000000000..51b1b6c737
--- /dev/null
+++ b/longest-consecutive-sequence/yuseok89.py
@@ -0,0 +1,18 @@
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        nums_unique = set(nums)
+
+        ans = 0
+
+        for num in nums_unique:
+            if (num - 1) in nums_unique:
+                continue
+
+            next = num + 1
+
+            while next in nums_unique:
+                next = next + 1
+
+            ans = max(ans, next - num)
+
+        return ans

From 4e4e41226157b830cd23f7acfae3c40f21d169f6 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 22:56:20 +0900
Subject: [PATCH 05/26] house robber solution

---
 house-robber/yuseok89.py | 11 +++++++++++
 1 file changed, 11 insertions(+)
 create mode 100644 house-robber/yuseok89.py

diff --git a/house-robber/yuseok89.py b/house-robber/yuseok89.py
new file mode 100644
index 0000000000..1fb92d3b85
--- /dev/null
+++ b/house-robber/yuseok89.py
@@ -0,0 +1,11 @@
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+
+        two_before, one_before = 0, 0
+
+        for num in nums:
+            cur = max(two_before + num, one_before)
+            two_before = one_before
+            one_before = cur
+
+        return max(one_before, two_before)

From 32cafb9bd6b4b597fd598b7d1c8ee79a11adff79 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 23 Jun 2026 23:06:02 +0900
Subject: [PATCH 06/26] add newline

---
 contains-duplicate/yuseok89.py           | 1 +
 house-robber/yuseok89.py                 | 1 +
 longest-consecutive-sequence/yuseok89.py | 1 +
 top-k-frequent-elements/yuseok89.py      | 1 +
 two-sum/yuseok89.py                      | 1 +
 5 files changed, 5 insertions(+)

diff --git a/contains-duplicate/yuseok89.py b/contains-duplicate/yuseok89.py
index 8648095834..4069db8cfd 100644
--- a/contains-duplicate/yuseok89.py
+++ b/contains-duplicate/yuseok89.py
@@ -9,3 +9,4 @@ def containsDuplicate(self, nums: List[int]) -> bool:
             dup_check.add(num)
 
         return False
+
diff --git a/house-robber/yuseok89.py b/house-robber/yuseok89.py
index 1fb92d3b85..cfda251e07 100644
--- a/house-robber/yuseok89.py
+++ b/house-robber/yuseok89.py
@@ -9,3 +9,4 @@ def rob(self, nums: List[int]) -> int:
             one_before = cur
 
         return max(one_before, two_before)
+
diff --git a/longest-consecutive-sequence/yuseok89.py b/longest-consecutive-sequence/yuseok89.py
index 51b1b6c737..9f1c9c8e1b 100644
--- a/longest-consecutive-sequence/yuseok89.py
+++ b/longest-consecutive-sequence/yuseok89.py
@@ -16,3 +16,4 @@ def longestConsecutive(self, nums: List[int]) -> int:
             ans = max(ans, next - num)
 
         return ans
+
diff --git a/top-k-frequent-elements/yuseok89.py b/top-k-frequent-elements/yuseok89.py
index bfaa5de681..89f682014d 100644
--- a/top-k-frequent-elements/yuseok89.py
+++ b/top-k-frequent-elements/yuseok89.py
@@ -26,3 +26,4 @@ def topKFrequent(self, nums: List[int], k: int) -> List[int]:
                 ret.append(num)
 
         return ret
+
diff --git a/two-sum/yuseok89.py b/two-sum/yuseok89.py
index 2033711307..c4ab442451 100644
--- a/two-sum/yuseok89.py
+++ b/two-sum/yuseok89.py
@@ -12,3 +12,4 @@ def twoSum(self, nums: List[int], target: int) -> List[int]:
                 return [idx, idx_map[need]]
 
         return []
+

From 49ecb593fae4f41ec5eaec4cd537a20976835602 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 25 Jun 2026 17:55:26 +0900
Subject: [PATCH 07/26] =?UTF-8?q?=EB=A6=AC=EB=B7=B0=20=EB=B0=98=EC=98=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 contains-duplicate/yuseok89.py           | 1 +
 house-robber/yuseok89.py                 | 1 +
 longest-consecutive-sequence/yuseok89.py | 1 +
 top-k-frequent-elements/yuseok89.py      | 1 +
 two-sum/yuseok89.py                      | 6 +++---
 5 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/contains-duplicate/yuseok89.py b/contains-duplicate/yuseok89.py
index 4069db8cfd..ec20f41283 100644
--- a/contains-duplicate/yuseok89.py
+++ b/contains-duplicate/yuseok89.py
@@ -1,3 +1,4 @@
+// TC: O(n), SC: O(n)
 class Solution:
     def containsDuplicate(self, nums: List[int]) -> bool:
         dup_check = set()
diff --git a/house-robber/yuseok89.py b/house-robber/yuseok89.py
index cfda251e07..f80ad1fd5d 100644
--- a/house-robber/yuseok89.py
+++ b/house-robber/yuseok89.py
@@ -1,3 +1,4 @@
+// TC: O(n), SC: O(1)
 class Solution:
     def rob(self, nums: List[int]) -> int:
 
diff --git a/longest-consecutive-sequence/yuseok89.py b/longest-consecutive-sequence/yuseok89.py
index 9f1c9c8e1b..6ced67e7f6 100644
--- a/longest-consecutive-sequence/yuseok89.py
+++ b/longest-consecutive-sequence/yuseok89.py
@@ -1,3 +1,4 @@
+// TC: O(n), SC: O(n)
 class Solution:
     def longestConsecutive(self, nums: List[int]) -> int:
         nums_unique = set(nums)
diff --git a/top-k-frequent-elements/yuseok89.py b/top-k-frequent-elements/yuseok89.py
index 89f682014d..735e8be199 100644
--- a/top-k-frequent-elements/yuseok89.py
+++ b/top-k-frequent-elements/yuseok89.py
@@ -1,3 +1,4 @@
+// TC: O(N + UlogK), SC: O(N)
 class Solution:
     def topKFrequent(self, nums: List[int], k: int) -> List[int]:
 
diff --git a/two-sum/yuseok89.py b/two-sum/yuseok89.py
index c4ab442451..25795b86c9 100644
--- a/two-sum/yuseok89.py
+++ b/two-sum/yuseok89.py
@@ -1,15 +1,15 @@
+// TC: O(N), SC: O(N)
 class Solution:
     def twoSum(self, nums: List[int], target: int) -> List[int]:
         idx_map = {}
 
-        for idx, num in enumerate(nums):
-            idx_map[num] = idx
-
         for idx, num in enumerate(nums):
             need = target - num
 
             if need in idx_map and idx != idx_map[need]:
                 return [idx, idx_map[need]]
 
+            idx_map[num] = idx
+
         return []
 

From a6fcc338d45e7f75ade275a10811bf5e3d04faf2 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 25 Jun 2026 23:03:24 +0900
Subject: [PATCH 08/26] =?UTF-8?q?=EB=A6=AC=EB=B7=B0=20=EB=B0=98=EC=98=81?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 contains-duplicate/yuseok89.py           | 3 ++-
 house-robber/yuseok89.py                 | 3 ++-
 longest-consecutive-sequence/yuseok89.py | 3 ++-
 top-k-frequent-elements/yuseok89.py      | 3 ++-
 two-sum/yuseok89.py                      | 3 ++-
 5 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/contains-duplicate/yuseok89.py b/contains-duplicate/yuseok89.py
index ec20f41283..6fa83a73ee 100644
--- a/contains-duplicate/yuseok89.py
+++ b/contains-duplicate/yuseok89.py
@@ -1,4 +1,5 @@
-// TC: O(n), SC: O(n)
+// TC: O(n)
+// SC: O(n)
 class Solution:
     def containsDuplicate(self, nums: List[int]) -> bool:
         dup_check = set()
diff --git a/house-robber/yuseok89.py b/house-robber/yuseok89.py
index f80ad1fd5d..46ef967c2c 100644
--- a/house-robber/yuseok89.py
+++ b/house-robber/yuseok89.py
@@ -1,4 +1,5 @@
-// TC: O(n), SC: O(1)
+// TC: O(n)
+// SC: O(1)
 class Solution:
     def rob(self, nums: List[int]) -> int:
 
diff --git a/longest-consecutive-sequence/yuseok89.py b/longest-consecutive-sequence/yuseok89.py
index 6ced67e7f6..224fd8b765 100644
--- a/longest-consecutive-sequence/yuseok89.py
+++ b/longest-consecutive-sequence/yuseok89.py
@@ -1,4 +1,5 @@
-// TC: O(n), SC: O(n)
+// TC: O(n)
+// SC: O(n)
 class Solution:
     def longestConsecutive(self, nums: List[int]) -> int:
         nums_unique = set(nums)
diff --git a/top-k-frequent-elements/yuseok89.py b/top-k-frequent-elements/yuseok89.py
index 735e8be199..2a3e09de76 100644
--- a/top-k-frequent-elements/yuseok89.py
+++ b/top-k-frequent-elements/yuseok89.py
@@ -1,4 +1,5 @@
-// TC: O(N + UlogK), SC: O(N)
+// TC: O(NlogK)
+// SC: O(N)
 class Solution:
     def topKFrequent(self, nums: List[int], k: int) -> List[int]:
 
diff --git a/two-sum/yuseok89.py b/two-sum/yuseok89.py
index 25795b86c9..b5465ca79c 100644
--- a/two-sum/yuseok89.py
+++ b/two-sum/yuseok89.py
@@ -1,4 +1,5 @@
-// TC: O(N), SC: O(N)
+// TC: O(N)
+// SC: O(N)
 class Solution:
     def twoSum(self, nums: List[int], target: int) -> List[int]:
         idx_map = {}

From 38a1f6799faf6a7c2eb01cfd7dadc1e33ed207ff Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 25 Jun 2026 23:43:03 +0900
Subject: [PATCH 09/26] =?UTF-8?q?=EA=B0=9C=EC=84=A0=20-=20AI=20assist?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 top-k-frequent-elements/yuseok89.py | 33 ++++++++++++-----------------
 1 file changed, 14 insertions(+), 19 deletions(-)

diff --git a/top-k-frequent-elements/yuseok89.py b/top-k-frequent-elements/yuseok89.py
index 2a3e09de76..ba1f1fd779 100644
--- a/top-k-frequent-elements/yuseok89.py
+++ b/top-k-frequent-elements/yuseok89.py
@@ -1,31 +1,26 @@
-// TC: O(NlogK)
+// TC: O(N)
 // SC: O(N)
 class Solution:
     def topKFrequent(self, nums: List[int], k: int) -> List[int]:
 
-        import heapq
+        cnt = Counter(nums)  # TC: O(n)
+        freq_map = defaultdict(list)
+        freq_max = 0
 
-        heap = []
-        cnt = {}
+        for num, freq in cnt.items():
+            freq_map[freq].append(num)
+            freq_max = max(freq_max, freq)
 
-        for num in nums:
-            if num not in cnt:
-                cnt[num] = 0
-
-            cnt[num] = cnt[num] + 1
+        ret = []
 
-        for num in cnt.keys():
-            if len(heap) < k:
-                heapq.heappush(heap, cnt[num])
-            elif heap[0] < cnt[num]:
-                heapq.heappop(heap)
-                heapq.heappush(heap, cnt[num])
+        for freq in range(freq_max, 0, -1):
+            if freq not in freq_map:
+                continue
 
-        ret = []
+            ret.extend(freq_map[freq])
 
-        for num in cnt.keys():
-            if cnt[num] >= heap[0]:
-                ret.append(num)
+            if len(ret) >= k:
+                break
 
         return ret
 

From 8bd5a3234eddb92d76d5b516e4cf7a1128fa8d80 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Mon, 29 Jun 2026 22:50:12 +0900
Subject: [PATCH 10/26] valid anagram solution

---
 valid-anagram/yuseok89.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 valid-anagram/yuseok89.py

diff --git a/valid-anagram/yuseok89.py b/valid-anagram/yuseok89.py
new file mode 100644
index 0000000000..b01f9d8a07
--- /dev/null
+++ b/valid-anagram/yuseok89.py
@@ -0,0 +1,13 @@
+## TC: O(N)
+## SC: O(1)
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+
+        if len(s) != len(t):
+            return False
+
+        cnt_s = Counter(s)
+        cnt_t = Counter(t)
+
+        return cnt_s == cnt_t
+

From cd23e3477799470f65c2405657fa4799c74bb630 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Mon, 29 Jun 2026 23:25:19 +0900
Subject: [PATCH 11/26] climbing stairs solution

---
 climbing-stairs/yuseok89.py | 15 +++++++++++++++
 valid-anagram/yuseok89.py   |  4 ++--
 2 files changed, 17 insertions(+), 2 deletions(-)
 create mode 100644 climbing-stairs/yuseok89.py

diff --git a/climbing-stairs/yuseok89.py b/climbing-stairs/yuseok89.py
new file mode 100644
index 0000000000..98908f9b6d
--- /dev/null
+++ b/climbing-stairs/yuseok89.py
@@ -0,0 +1,15 @@
+# TC: O(N)
+# SC: O(1)
+class Solution:
+    def climbStairs(self, n: int) -> int:
+
+        one_down = 1
+        two_down = 0
+
+        for _ in range(1, n):
+            cur = two_down + one_down
+            two_down = one_down
+            one_down = cur
+
+        return two_down + one_down
+
diff --git a/valid-anagram/yuseok89.py b/valid-anagram/yuseok89.py
index b01f9d8a07..1d40aed598 100644
--- a/valid-anagram/yuseok89.py
+++ b/valid-anagram/yuseok89.py
@@ -1,5 +1,5 @@
-## TC: O(N)
-## SC: O(1)
+# TC: O(N)
+# SC: O(K)
 class Solution:
     def isAnagram(self, s: str, t: str) -> bool:
 

From 120df1f0479b013444edafaab50a80f096e9e5e5 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 1 Jul 2026 09:50:50 +0900
Subject: [PATCH 12/26] product of array except self solution

---
 product-of-array-except-self/yuseok89.py | 25 ++++++++++++++++++++++++
 1 file changed, 25 insertions(+)
 create mode 100644 product-of-array-except-self/yuseok89.py

diff --git a/product-of-array-except-self/yuseok89.py b/product-of-array-except-self/yuseok89.py
new file mode 100644
index 0000000000..7a4cd4bb3b
--- /dev/null
+++ b/product-of-array-except-self/yuseok89.py
@@ -0,0 +1,25 @@
+// TC: O(N)
+// SC: O(N)
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+
+        n = len(nums)
+        prefix_prod = [0] * n
+        suffix_prod = [0] * n
+
+        prefix_prod[0] = nums[0]
+        suffix_prod[-1] = nums[-1]
+
+        for idx in range(1, n):
+            prefix_prod[idx] = prefix_prod[idx - 1] * nums[idx]
+            suffix_prod[-idx - 1] = suffix_prod[-idx] * nums[-idx - 1]
+
+        ret = []
+
+        ret.append(suffix_prod[1])
+        for idx in range(1, n - 1):
+            ret.append(prefix_prod[idx - 1] * suffix_prod[idx + 1])
+        ret.append(prefix_prod[n - 2])
+
+        return ret
+

From 1d4ff54af3cf097c58c1cff5b84bbf925b2ac5ea Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 1 Jul 2026 10:34:53 +0900
Subject: [PATCH 13/26] 3sum solution

---
 3sum/yuseok89.py                         | 33 ++++++++++++++++++++++++
 product-of-array-except-self/yuseok89.py |  4 +--
 2 files changed, 35 insertions(+), 2 deletions(-)
 create mode 100644 3sum/yuseok89.py

diff --git a/3sum/yuseok89.py b/3sum/yuseok89.py
new file mode 100644
index 0000000000..52d477339f
--- /dev/null
+++ b/3sum/yuseok89.py
@@ -0,0 +1,33 @@
+# TC: O(N^2)
+# SC: O(N)
+class Solution:
+    def threeSum(self, nums: list[int]) -> list[list[int]]:
+
+        cnt_dict = Counter(nums)
+        nums_uniq = sorted(cnt_dict.keys())
+        n = len(nums_uniq)
+
+        ret = []
+
+        for num in cnt_dict.keys():
+            if num == 0:
+                if cnt_dict[num] >= 3:
+                    ret.append([0, 0, 0])
+            elif cnt_dict[num] >= 2 and num * 2 * -1 in cnt_dict:
+                ret.append([num, num, num * 2 * -1])
+
+        for idx1, num1 in enumerate(nums_uniq):
+            if num1 > 0:
+                break
+
+            for idx2 in range(idx1 + 1, n):
+                num2 = nums_uniq[idx2]
+                num3 = (num1 + num2) * -1
+
+                if num2 >= num3:
+                    break
+                elif num3 in cnt_dict:
+                    ret.append([num1, num2, num3])
+
+        return ret
+
diff --git a/product-of-array-except-self/yuseok89.py b/product-of-array-except-self/yuseok89.py
index 7a4cd4bb3b..2acceaf3c5 100644
--- a/product-of-array-except-self/yuseok89.py
+++ b/product-of-array-except-self/yuseok89.py
@@ -1,5 +1,5 @@
-// TC: O(N)
-// SC: O(N)
+# TC: O(N)
+# SC: O(N)
 class Solution:
     def productExceptSelf(self, nums: List[int]) -> List[int]:
 

From 23142a79ef3d5f6ec82389e38d51ded81d205130 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 1 Jul 2026 10:52:46 +0900
Subject: [PATCH 14/26] validate binary search tree solution

---
 validate-binary-search-tree/yuseok89.py | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)
 create mode 100644 validate-binary-search-tree/yuseok89.py

diff --git a/validate-binary-search-tree/yuseok89.py b/validate-binary-search-tree/yuseok89.py
new file mode 100644
index 0000000000..9f1601f00b
--- /dev/null
+++ b/validate-binary-search-tree/yuseok89.py
@@ -0,0 +1,23 @@
+# TC: O(N)
+# SC: O(1)
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+
+    def isValid(self, left_bound, right_bound, root):
+        if root is None:
+            return True
+        if left_bound is not None and left_bound >= root.val:
+            return False
+        if right_bound is not None and right_bound <= root.val:
+            return False
+
+        return self.isValid(left_bound, root.val, root.left) and self.isValid(root.val, right_bound, root.right)
+
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        return self.isValid(None, root.val, root.left) and self.isValid(root.val, None, root.right)
+

From 0cb14caa06d27da29b7434e29ab8e9434db7c2c3 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 1 Jul 2026 11:29:40 +0900
Subject: [PATCH 15/26] =?UTF-8?q?=EA=B3=B5=EA=B0=84=EB=B3=B5=EC=9E=A1?=
 =?UTF-8?q?=EB=8F=84=20=EC=97=85=EB=8D=B0=EC=9D=B4=ED=8A=B8?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 validate-binary-search-tree/yuseok89.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/validate-binary-search-tree/yuseok89.py b/validate-binary-search-tree/yuseok89.py
index 9f1601f00b..0e9cc2015d 100644
--- a/validate-binary-search-tree/yuseok89.py
+++ b/validate-binary-search-tree/yuseok89.py
@@ -1,5 +1,5 @@
 # TC: O(N)
-# SC: O(1)
+# SC: O(H)
 # Definition for a binary tree node.
 # class TreeNode:
 #     def __init__(self, val=0, left=None, right=None):

From 9465142cf0b49c73828130b336a370cd153879db Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 1 Jul 2026 13:24:59 +0900
Subject: [PATCH 16/26] =?UTF-8?q?=EA=B3=B5=EA=B0=84=EB=B3=B5=EC=9E=A1?=
 =?UTF-8?q?=EB=8F=84=20=EC=97=85=EB=8D=B0=EC=9D=B4=ED=8A=B8?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 valid-anagram/yuseok89.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/valid-anagram/yuseok89.py b/valid-anagram/yuseok89.py
index 1d40aed598..f8793092e7 100644
--- a/valid-anagram/yuseok89.py
+++ b/valid-anagram/yuseok89.py
@@ -1,5 +1,5 @@
 # TC: O(N)
-# SC: O(K)
+# SC: O(1)
 class Solution:
     def isAnagram(self, s: str, t: str) -> bool:
 

From 4b09054de351728b6558c4fc8e2d63009307293e Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 7 Jul 2026 23:16:06 +0900
Subject: [PATCH 17/26] validate palindrome solution

---
 valid-palindrome/yuseok89.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 valid-palindrome/yuseok89.py

diff --git a/valid-palindrome/yuseok89.py b/valid-palindrome/yuseok89.py
new file mode 100644
index 0000000000..803ee69342
--- /dev/null
+++ b/valid-palindrome/yuseok89.py
@@ -0,0 +1,17 @@
+# TC: O(N)
+# SC: O(1)
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+
+        import re
+
+        s = re.sub(r'[^a-zA-Z0-9]', '', s.lower())
+
+        n = len(s)
+
+        for idx in range(0, n // 2):
+            if s[idx] != s[n - idx - 1]:
+                return False
+
+        return True
+

From da3aad9b94b888724f7c02b4fb7a49ac75e78896 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 7 Jul 2026 23:17:03 +0900
Subject: [PATCH 18/26] number of 1 bits solution

---
 number-of-1-bits/yuseok89.py | 13 +++++++++++++
 1 file changed, 13 insertions(+)
 create mode 100644 number-of-1-bits/yuseok89.py

diff --git a/number-of-1-bits/yuseok89.py b/number-of-1-bits/yuseok89.py
new file mode 100644
index 0000000000..a70faf428e
--- /dev/null
+++ b/number-of-1-bits/yuseok89.py
@@ -0,0 +1,13 @@
+# TC: O(logN)
+# SC: O(1)
+class Solution:
+    def hammingWeight(self, n: int) -> int:
+
+        cnt = 0
+
+        while n > 0:
+            cnt = cnt + (n % 2)
+            n //= 2
+
+        return cnt
+

From 5c4d5fb201a71ff3f487ff62656673b9c7711847 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 7 Jul 2026 23:20:41 +0900
Subject: [PATCH 19/26] combination sum solution

---
 combination-sum/yuseok89.py | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100644 combination-sum/yuseok89.py

diff --git a/combination-sum/yuseok89.py b/combination-sum/yuseok89.py
new file mode 100644
index 0000000000..b6c087d60c
--- /dev/null
+++ b/combination-sum/yuseok89.py
@@ -0,0 +1,27 @@
+# TC: O(NlogN)
+# SC: O(logN)
+class Solution:
+
+    def rec(self, cur, candi, combi, sum, target, ans):
+
+        if sum == target:
+            ans.append(combi)
+
+            return
+
+        for idx in range(cur, len(candi)):
+
+            multi = 1
+
+            while sum + multi * candi[idx] <= target:
+                self.rec(idx + 1, candi, combi + [candi[idx]] * multi, sum + multi * candi[idx], target, ans)
+                multi += 1
+
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+
+        ans = []
+
+        self.rec(0, candidates, [], 0, target, ans)
+
+        return ans
+

From 03f3f1a86cbba6092791e8c70b7ddab3a76b00f1 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 7 Jul 2026 23:21:51 +0900
Subject: [PATCH 20/26] decode ways solution

---
 decode-ways/yuseok89.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 decode-ways/yuseok89.py

diff --git a/decode-ways/yuseok89.py b/decode-ways/yuseok89.py
new file mode 100644
index 0000000000..da6c0da328
--- /dev/null
+++ b/decode-ways/yuseok89.py
@@ -0,0 +1,29 @@
+# TC: O(N)
+# SC: O(N)
+class Solution:
+
+    memo = []
+
+    def rec(self, idx, s, n):
+        if self.memo[idx] == -1:
+
+            cnt = 0
+
+            if int(s[idx]) != 0:
+                cnt += self.rec(idx + 1, s, n)
+
+            if idx + 1 < n:
+                if int(s[idx]) != 0 and int(s[idx]) * 10 + int(s[idx + 1]) <= 26:
+                    cnt += self.rec(idx + 2, s, n)
+
+            self.memo[idx] = cnt
+
+        return self.memo[idx]
+
+    def numDecodings(self, s: str) -> int:
+
+        self.memo = [-1] * (len(s) + 1)
+        self.memo[len(s)] = 1
+
+        return self.rec(0, s, len(s))
+

From d8d5ea42a16b07442940b3c273c71cc8f1ad5312 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Tue, 7 Jul 2026 23:22:50 +0900
Subject: [PATCH 21/26] maximum subarray solution

---
 maximum-subarray/yuseok89.py | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)
 create mode 100644 maximum-subarray/yuseok89.py

diff --git a/maximum-subarray/yuseok89.py b/maximum-subarray/yuseok89.py
new file mode 100644
index 0000000000..e56c8f9e4f
--- /dev/null
+++ b/maximum-subarray/yuseok89.py
@@ -0,0 +1,17 @@
+# TC: O(N)
+# SC: O(1)
+class Solution:
+    def maxSubArray(self, nums: List[int]) -> int:
+        sum = nums[0] if nums[0] < 0 else 0
+        ans = sum
+
+        for num in nums:
+            if num > sum + num:
+                sum = num
+            else:
+                sum += num
+
+            ans = max(ans, sum)
+
+        return ans
+

From 1f003e2d4777b9cfb3fa4c60395b2520fd27643f Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Wed, 8 Jul 2026 00:35:01 +0900
Subject: [PATCH 22/26] =?UTF-8?q?=EB=B3=B5=EC=9E=A1=EB=8F=84=20=EC=97=85?=
 =?UTF-8?q?=EB=8D=B0=EC=9D=B4=ED=8A=B8?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 combination-sum/yuseok89.py | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/combination-sum/yuseok89.py b/combination-sum/yuseok89.py
index b6c087d60c..59f4bf2eed 100644
--- a/combination-sum/yuseok89.py
+++ b/combination-sum/yuseok89.py
@@ -1,5 +1,5 @@
-# TC: O(NlogN)
-# SC: O(logN)
+# TC: O(K*N!)
+# SC: O(K)
 class Solution:
 
     def rec(self, cur, candi, combi, sum, target, ans):

From a022d1040a0a1926e24c26c3ceb3de35b8a7a721 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 9 Jul 2026 20:07:01 +0900
Subject: [PATCH 23/26] =?UTF-8?q?=EC=9E=AC=EA=B7=80=20=EB=A1=9C=EC=A7=81?=
 =?UTF-8?q?=20=EA=B0=9C=EC=84=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 combination-sum/yuseok89.py | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/combination-sum/yuseok89.py b/combination-sum/yuseok89.py
index 59f4bf2eed..6003c0fc24 100644
--- a/combination-sum/yuseok89.py
+++ b/combination-sum/yuseok89.py
@@ -1,27 +1,28 @@
-# TC: O(K*N!)
-# SC: O(K)
+# TC: O(N^T)
+# SC: O(T)
 class Solution:
 
-    def rec(self, cur, candi, combi, sum, target, ans):
+    def rec(self, cur_idx, target, candi, cur_combi, ans):
 
-        if sum == target:
-            ans.append(combi)
+        if target == 0:
+            ans.append(cur_combi.copy())
 
+        if cur_idx == len(candi):
             return
 
-        for idx in range(cur, len(candi)):
+        for idx in range(cur_idx, len(candi)):
+            if target < candi[idx]:
+                continue
 
-            multi = 1
-
-            while sum + multi * candi[idx] <= target:
-                self.rec(idx + 1, candi, combi + [candi[idx]] * multi, sum + multi * candi[idx], target, ans)
-                multi += 1
+            cur_combi.append(candi[idx])
+            self.rec(idx, target - candi[idx], candi, cur_combi, ans)
+            cur_combi.pop()
 
     def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
 
         ans = []
 
-        self.rec(0, candidates, [], 0, target, ans)
+        self.rec(0, target, candidates, [], ans)
 
         return ans
 

From b8248c42f5d47b02e22f8a884eca32822396fecb Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 9 Jul 2026 20:19:29 +0900
Subject: [PATCH 24/26] =?UTF-8?q?maximum=20subarray=20=ED=92=80=EC=9D=B4?=
 =?UTF-8?q?=20=EA=B0=9C=EC=84=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 maximum-subarray/yuseok89.py | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/maximum-subarray/yuseok89.py b/maximum-subarray/yuseok89.py
index e56c8f9e4f..b8c10491dd 100644
--- a/maximum-subarray/yuseok89.py
+++ b/maximum-subarray/yuseok89.py
@@ -6,12 +6,19 @@ def maxSubArray(self, nums: List[int]) -> int:
         ans = sum
 
         for num in nums:
-            if num > sum + num:
-                sum = num
-            else:
-                sum += num
-
+            sum = max(num, sum + num)
             ans = max(ans, sum)
 
         return ans
 
+# class Solution:
+#     def maxSubArray(self, nums: List[int]) -> int:
+#         sum = nums[0]
+#         ans = sum
+
+#         for idx in range(1, len(nums)):
+#             sum = max(nums[idx], sum + nums[idx])
+#             ans = max(ans, sum)
+
+#         return ans
+

From 51c1012373a7f2a0eea69b9fd14b6954c87b7a44 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 9 Jul 2026 20:29:11 +0900
Subject: [PATCH 25/26] =?UTF-8?q?valid=20palindrome=20=ED=92=80=EC=9D=B4?=
 =?UTF-8?q?=20=EA=B0=9C=EC=84=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 valid-palindrome/yuseok89.py | 36 +++++++++++++++++++++++++++++++-----
 1 file changed, 31 insertions(+), 5 deletions(-)

diff --git a/valid-palindrome/yuseok89.py b/valid-palindrome/yuseok89.py
index 803ee69342..4af870bc87 100644
--- a/valid-palindrome/yuseok89.py
+++ b/valid-palindrome/yuseok89.py
@@ -1,17 +1,43 @@
 # TC: O(N)
 # SC: O(1)
 class Solution:
+
+    def is_alphanum(self, c):
+        return 'a' <= c <= 'z' or '0' <= c <= '9'
+
     def isPalindrome(self, s: str) -> bool:
 
-        import re
+        left = 0
+        right = len(s) - 1
 
-        s = re.sub(r'[^a-zA-Z0-9]', '', s.lower())
+        s = s.lower()
 
-        n = len(s)
+        while(left < right):
+            while left < len(s) and not self.is_alphanum(s[left]):
+                left += 1
+            while right >= 0 and not self.is_alphanum(s[right]):
+                right -= 1
 
-        for idx in range(0, n // 2):
-            if s[idx] != s[n - idx - 1]:
+            if left < right and s[left] != s[right]:
                 return False
 
+            left += 1
+            right -= 1
+
         return True
 
+# class Solution:
+#     def isPalindrome(self, s: str) -> bool:
+#
+#         import re
+#
+#         s = re.sub(r'[^a-zA-Z0-9]', '', s.lower())
+#
+#         n = len(s)
+#
+#         for idx in range(0, n // 2):
+#             if s[idx] != s[n - idx - 1]:
+#                 return False
+#
+#         return True
+

From 65431c08ae2c95174a9380505e43e75ddf08b4e4 Mon Sep 17 00:00:00 2001
From: Yuseok Jo <yuseok89@gmail.com>
Date: Thu, 9 Jul 2026 20:38:37 +0900
Subject: [PATCH 26/26] =?UTF-8?q?maximum=20subarray=20=ED=92=80=EC=9D=B4?=
 =?UTF-8?q?=20=EA=B0=9C=EC=84=A0?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 maximum-subarray/yuseok89.py | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/maximum-subarray/yuseok89.py b/maximum-subarray/yuseok89.py
index b8c10491dd..0056aae9be 100644
--- a/maximum-subarray/yuseok89.py
+++ b/maximum-subarray/yuseok89.py
@@ -2,10 +2,10 @@
 # SC: O(1)
 class Solution:
     def maxSubArray(self, nums: List[int]) -> int:
-        sum = nums[0] if nums[0] < 0 else 0
+        sum = nums[0]
         ans = sum
 
-        for num in nums:
+        for num in nums[1:]:
             sum = max(num, sum + num)
             ans = max(ans, sum)
 
@@ -13,11 +13,11 @@ def maxSubArray(self, nums: List[int]) -> int:
 
 # class Solution:
 #     def maxSubArray(self, nums: List[int]) -> int:
-#         sum = nums[0]
+#         sum = nums[0] if nums[0] < 0 else 0
 #         ans = sum
 
-#         for idx in range(1, len(nums)):
-#             sum = max(nums[idx], sum + nums[idx])
+#         for num in nums:
+#             sum = max(num, sum + num)
 #             ans = max(ans, sum)
 
 #         return ans