Add top k frequent elements solution

Author: sudheerj

src/java1/algorithms/heap/TopKFrequentElements.java

@@ -0,0 +1,37 @@
+package java1.algorithms.heap;
+
+import java.util.*;
+
+public class TopKFrequentElements {
+    // TC: O(n logk) SC: O(n)
+    private int[] topKFrequent(int[] nums, int k){
+        int[] topElements = new int[k];
+        HashMap<Integer, Integer> freqMap = new HashMap<>();
+        for(int num: nums){
+            freqMap.put(num, freqMap.getOrDefault(num, 0) +1);
+        }
+
+        PriorityQueue<Map.Entry<Integer, Integer>> queue = new PriorityQueue<>(
+            (a, b) -> a.getValue()-b.getValue()
+        );
+
+        for(Map.Entry<Integer, Integer> it: freqMap.entrySet()){
+            queue.add(it);
+            if(queue.size() > k) queue.poll();
+        }
+
+        int i = k;
+        while (!queue.isEmpty()) {
+            topElements[--i] = queue.poll().getKey();
+        }
+
+        return topElements;
+    }
+
+    public static void main(String[] args) {
+        int[] nums = {1,1,1,2,2,3};
+        int k = 2;
+        TopKFrequentElements elements = new TopKFrequentElements();
+        System.out.println(Arrays.toString(elements.topKFrequent(nums, k)));
+    }
+}