From 8acdf4b33fd483ed7c7ad0c28fca0e66441ff2b9 Mon Sep 17 00:00:00 2001
From: doh6077 <kimdohee@sheridancollege.ca>
Date: Fri, 14 Nov 2025 19:18:28 -0500
Subject: [PATCH 1/3] Top K Frequent Elements solution

---
 top-k-frequent-elements/doh6077.py | 12 ++++++++++++
 1 file changed, 12 insertions(+)
 create mode 100644 top-k-frequent-elements/doh6077.py

diff --git a/top-k-frequent-elements/doh6077.py b/top-k-frequent-elements/doh6077.py
new file mode 100644
index 0000000000..d5d1d11a6a
--- /dev/null
+++ b/top-k-frequent-elements/doh6077.py
@@ -0,0 +1,12 @@
+class Solution:
+    # dictionary use 
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        result = {}  # key: 원소, value: 등장 횟수
+        for n in nums:
+            if n in result:
+                result[n] = result[n] + 1
+            else:
+                result[n] = 1
+
+        # 가장 자주 등장한 원소 k개 반환
+        return sorted(result.keys(), key=lambda x: result[x], reverse=True)[:k]

From 4aa739c525e53f69924afbc2eaf7b1dee5672476 Mon Sep 17 00:00:00 2001
From: doh6077 <kimdohee@sheridancollege.ca>
Date: Fri, 21 Nov 2025 14:59:07 -0500
Subject: [PATCH 2/3] 3Sum Solution

---
 3sum/doh6077.py | 42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)
 create mode 100644 3sum/doh6077.py

diff --git a/3sum/doh6077.py b/3sum/doh6077.py
new file mode 100644
index 0000000000..44b2d4435c
--- /dev/null
+++ b/3sum/doh6077.py
@@ -0,0 +1,42 @@
+from typing import List
+
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        n = len(nums)
+        res: List[List[int]] = []
+
+        for i in range(n - 2):
+            # i 중복 스킵
+            if i > 0 and nums[i] == nums[i - 1]:
+                continue
+
+            # nums[i] 이후는 전부 양수 → 더 이상 0 못 만듦
+            if nums[i] > 0:
+                break
+
+            left, right = i + 1, n - 1
+
+            while left < right:
+                total = nums[i] + nums[left] + nums[right]
+
+                if total == 0:
+                    res.append([nums[i], nums[left], nums[right]])
+
+                    left += 1
+                    right -= 1
+
+                    # left 중복 스킵
+                    while left < right and nums[left] == nums[left - 1]:
+                        left += 1
+
+                    # right 중복 스킵
+                    while left < right and nums[right] == nums[right + 1]:
+                        right -= 1
+
+                elif total < 0:
+                    left += 1
+                else:
+                    right -= 1
+
+        return res

From fe26eb0cb575ff5cd1fac88b8ee5203ff805ede4 Mon Sep 17 00:00:00 2001
From: doh6077 <kimdohee@sheridancollege.ca>
Date: Fri, 21 Nov 2025 16:52:54 -0500
Subject: [PATCH 3/3] Validate Binary Search Tree Solution

---
 validate-binary-search-tree/doh6077.py | 10 ++++++++++
 1 file changed, 10 insertions(+)
 create mode 100644 validate-binary-search-tree/doh6077.py

diff --git a/validate-binary-search-tree/doh6077.py b/validate-binary-search-tree/doh6077.py
new file mode 100644
index 0000000000..2d3288d202
--- /dev/null
+++ b/validate-binary-search-tree/doh6077.py
@@ -0,0 +1,10 @@
+class Solution:
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        def validate(node: Optional[TreeNode], low: float, high: float) -> bool:
+            if not node:
+                return True
+            if not (low < node.val < high):
+                return False
+            return (validate(node.left, low, node.val) and
+                    validate(node.right, node.val, high))
+        return validate(root, float('-inf'), float('inf'))