diff --git a/src/my_project/interviews/top_150_questions_round_20/contains_duplicates.py b/src/my_project/interviews/top_150_questions_round_20/contains_duplicates.py
new file mode 100644
index 00000000..3247a3ff
--- /dev/null
+++ b/src/my_project/interviews/top_150_questions_round_20/contains_duplicates.py
@@ -0,0 +1,22 @@
+from typing import List, Union, Collection, Mapping, Optional
+from abc import ABC, abstractmethod
+from collections import defaultdict
+
+class Solution:
+    def containsNearbyDuplicate(self, nums: List[int], k: int) -> bool:
+
+        answer_dic = defaultdict(int)
+        len_nums = len(nums)
+
+        for i in range(len_nums):
+
+            answer_dic[nums[i]] += 1
+
+            if i > k: 
+                answer_dic[nums[i - (k+1)]] -= 1
+
+            if answer_dic[nums[i]] > 1: 
+                return True 
+            
+        return False 
+
diff --git a/tests/test_150_questions_round_20/test_contains_duplicates_round_20.py b/tests/test_150_questions_round_20/test_contains_duplicates_round_20.py
new file mode 100644
index 00000000..2f17a55a
--- /dev/null
+++ b/tests/test_150_questions_round_20/test_contains_duplicates_round_20.py
@@ -0,0 +1,15 @@
+import unittest
+from src.my_project.interviews.top_150_questions_round_20\
+.contains_duplicates import Solution
+
+class ContainsDuplicatesTestCase(unittest.TestCase):
+
+    def test_contains_duplicates(self):
+        solution = Solution()
+        output = solution.containsNearbyDuplicate(nums=[1,2,3,1], k=3)
+        self.assertTrue(output)
+
+    def test_contains_no_duplicates(self):
+        solution = Solution()
+        output = solution.containsNearbyDuplicate(nums=[1,2,3,1,2,3], k=2)
+        self.assertFalse(output)
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