Add top K frequent elements solution

Author: hyunjung-choi

top-k-frequent-elements/hyunjung-choi.kt

@@ -0,0 +1,12 @@
+class Solution {
+    fun topKFrequent(nums: IntArray, k: Int): IntArray {
+        val frequency = nums.toList().groupingBy { it }.eachCount()
+
+        return frequency
+            .toList()
+            .sortedByDescending { it.second }
+            .take(k)
+            .map { it.first }
+            .toIntArray()
+    }
+}