diff --git a/3sum/hestia-park.py b/3sum/hestia-park.py
new file mode 100644
index 000000000..565abffa3
--- /dev/null
+++ b/3sum/hestia-park.py
@@ -0,0 +1,25 @@
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        answer=set()
+        for i in range(len(nums)):
+            if nums[i] > 0:
+                break  # 이후 숫자는 모두 양수 → 합이 0 불가능
+            if i > 0 and nums[i] == nums[i - 1]:  
+                continue
+
+            left, right = i + 1, len(nums) - 1
+            while left < right:
+                term = nums[i] + nums[left] + nums[right]
+                if term == 0:
+                    answer.add((nums[i], nums[left], nums[right]))
+                    left += 1
+                    right -= 1
+                elif term < 0:
+                    left += 1
+                else:
+                    right -= 1
+
+        return [list(triplet) for triplet in answer]
+
+
diff --git a/climbing-stairs/hestia-park.py b/climbing-stairs/hestia-park.py
new file mode 100644
index 000000000..56bad6352
--- /dev/null
+++ b/climbing-stairs/hestia-park.py
@@ -0,0 +1,21 @@
+class Solution:
+    def climbStairs(self, n: int) -> int:
+            if n <= 1:
+                return 1
+
+            # dp = [0] * (n + 1)
+            # dp[0] = 1
+            # dp[1] = 1
+
+            # for i in range(2, n + 1):
+            #     dp[i] = dp[i - 1] + dp[i - 2]
+
+            # return dp[n]
+            # optima sol
+            dp_0,dp_1=1,1
+            for _ in range(2,n+1):
+                dp_0,dp_1=dp_1,dp_0+dp_1
+            return dp_1
+
+
+
diff --git a/contains-duplicate/hestia-park.py b/contains-duplicate/hestia-park.py
new file mode 100644
index 000000000..d41e60eb0
--- /dev/null
+++ b/contains-duplicate/hestia-park.py
@@ -0,0 +1,5 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        return len(nums) != len(set(nums))
+
+    
diff --git a/product-of-array-except-self/hestia-park.py b/product-of-array-except-self/hestia-park.py
new file mode 100644
index 000000000..e7f8c4e60
--- /dev/null
+++ b/product-of-array-except-self/hestia-park.py
@@ -0,0 +1,17 @@
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n=len(nums)
+        answer=[1] * n
+        #for left
+        for i in range(1,n):
+            answer[i]=answer[i-1]*nums[i-1]
+        
+        tail=1
+        #for right 
+        for i in range(n-1,-1,-1):
+            answer[i] *= tail
+            tail *= nums[i]
+        return answer
+
+
+
diff --git a/valid-anagram/hestia-park.py b/valid-anagram/hestia-park.py
new file mode 100644
index 000000000..dc1ae53fe
--- /dev/null
+++ b/valid-anagram/hestia-park.py
@@ -0,0 +1,9 @@
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        if len(s) != len(t):
+            return False
+        counter_s=Counter(s)
+        counter_t=Counter(t)
+        return counter_s == counter_t
+
+
diff --git a/validate-binary-search-tree/hestia-park.py b/validate-binary-search-tree/hestia-park.py
new file mode 100644
index 000000000..b4df31bb0
--- /dev/null
+++ b/validate-binary-search-tree/hestia-park.py
@@ -0,0 +1,12 @@
+class Solution:
+    def isValidBST(self, root: Optional[TreeNode]) -> bool:
+        def check(node, min_val, max_val):
+            if not node:
+                return True
+            if not (min_val < node.val < max_val):
+                return False
+            return check(node.left, min_val, node.val) and check(node.right, node.val, max_val)
+        
+        return check(root, float('-inf'), float('inf'))
+
+