347. Top K Frequent Elements

Aug 12

Author: TonyKim9401

top-k-frequent-elements/TonyKim9401.java

@@ -0,0 +1,32 @@
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+
+        // declare hashmap 
+        // key: each element, value: appered count
+        Map<Integer, Integer> map = new HashMap<>();
+
+        // if map contains the element, increase its value by one.
+        // else put the element and 1 for initializing
+        for (int num : nums) {
+            if (map.containsKey(num)) {
+                map.put(num, map.getOrDefault(num, 0) + 1);
+            } else {
+                map.put(num, 1);
+            }
+        }
+
+        // keyList only has key values of the hashmap
+        // using their value count sort keys by descending order
+        List<Integer> keyList = new ArrayList<>(map.keySet());
+        Collections.sort(keyList, (o1, o2) -> map.get(o2).compareTo(map.get(o1)));
+
+
+        int[] output = new int[k];
+        int idx = 0;
+
+        // retreive keys k times and set output
+        while (idx < k) output[idx] = keyList.get(idx++);
+
+        return output;
+    }
+}