diff --git a/3sum/paran22.py b/3sum/paran22.py
new file mode 100644
index 000000000..46c2afc08
--- /dev/null
+++ b/3sum/paran22.py
@@ -0,0 +1,24 @@
+class Solution:
+    # time complexity: O(n^2)
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        nums.sort()
+        answer = set()
+
+        for i in range(len(nums) - 2):
+            if i > 0 and nums[i] == nums[i - 1]:
+                continue
+
+            left, right = i + 1, len(nums) - 1
+            while left < right:
+                sum = nums[i] + nums[left] + nums[right]
+                if sum == 0:
+                    answer.add((nums[i], nums[left], nums[right]))
+                    left += 1
+                    right -= 1
+                elif sum > 0:
+                    right -= 1
+                elif sum < 0:
+                    left += 1
+
+        return [list(x) for x in answer]
+
diff --git a/climbing-stairs/paran22.py b/climbing-stairs/paran22.py
new file mode 100644
index 000000000..760c39966
--- /dev/null
+++ b/climbing-stairs/paran22.py
@@ -0,0 +1,11 @@
+class Solution:
+    # time complexity: O(n)
+    def climbStairs(self, n: int) -> int:
+        if n <= 2:
+            return n
+    
+        prev1, prev2 = 1, 2
+        for _ in range(3, n + 1):
+            current = prev1 + prev2
+            prev1, prev2 = prev2, current
+        return prev2
diff --git a/product-of-array-except-self/paran22.py b/product-of-array-except-self/paran22.py
new file mode 100644
index 000000000..56e6eef88
--- /dev/null
+++ b/product-of-array-except-self/paran22.py
@@ -0,0 +1,18 @@
+class Solution:
+    # time complexity: O(n)
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        answer = [1] * n
+
+        prefix = 1
+        for i in range(n):
+            answer[i] = prefix
+            prefix *= nums[i]
+
+        suffix = 1
+        for i in range(n-1, -1, -1):
+            answer[i] *= suffix
+            suffix *= nums[i]
+
+        return answer
+    
diff --git a/valid-anagram/paran22.py b/valid-anagram/paran22.py
new file mode 100644
index 000000000..46c71857f
--- /dev/null
+++ b/valid-anagram/paran22.py
@@ -0,0 +1,7 @@
+from collections import Counter
+
+class Solution:
+    # time complexity: O(n)
+    def isAnagram(self, s: str, t: str) -> bool:
+        return Counter(s) == Counter(t)
+