add solution top k frequent elements

Author: rivkode

top-k-frequent-elements/JonghunLee.py

@@ -0,0 +1,41 @@
+from typing import List
+
+# Time Complexity O(n log n)
+# - traversing for loop takes O(n) to create hash dictionary,
+# - and when sorting by sorted function(TimSort) it takes O(nlogn)
+# Space Complexity O(n log n)
+# - creating hash dictionary takes O(n)
+# - and when sorting takes O(n), hash[x] occupy O(1)
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        hash = dict()
+
+        # for loop nums to set count for each element in hash(dictionary)
+        for num in nums:
+            if num in hash:
+                hash[num] += 1
+            else:
+                hash[num] = 1
+
+        # sort (TimSort), using lambda function to set a sorting key which is a count
+        return sorted(hash, key=lambda x: hash[x], reverse=True)[:k]
+
+if __name__ == "__main__":
+    solution = Solution()
+
+    # test case
+    nums_list = [
+        [1,1,1,2,2,3], # [1, 2]
+        [1] # [1]
+    ]
+    k_list = [2, 1]
+
+    for i in range(2):
+        nums = nums_list[i]
+        k = k_list[i]
+        result = solution.topKFrequent(nums, k)
+        print(f"start{i}")
+        print(f"input : {nums}, {k}")
+        print(f"result : {result}")
+