diff --git a/contains-duplicate/yerim01.py b/contains-duplicate/yerim01.py
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+# Leetcode 217: https://leetcode.com/problems/contains-duplicate/description/
+# Goal: Given an array of integers,
+# return True if the array has duplicates or return False if all elements are distinct.
+# Approach:
+# - Use a hash set to track elements we have already seen.
+# - Iterate through the array and if the current number already exists in the set, return True.
+# - Otherwise, add the current number to the set.
+# Time complexity: O(n)
+# - We iterate through the array once.
+# Space complexity: O(n)
+# - We store all elements in the set in the worst case.
+
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        h = set()
+
+        for n in nums:
+            if n not in h:
+                h.add(n)
+            else:
+                return True
+        return False