add solution of top-k-frequent-elements

Author: jinhyungrhee

top-k-frequent-elements/jinhyungrhee.java

@@ -0,0 +1,29 @@
+import java.util.*;
+import java.util.stream.*;
+
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+
+        Map<Integer, Integer> map = new HashMap<>();
+        for(int n : nums) {
+            if(!map.containsKey(n)) {
+                map.put(n, 1);
+            } else {
+                map.put(n, map.get(n) + 1);
+            }
+        }
+
+        Map<Integer, Integer> sortedMap = map.entrySet().stream()
+                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))
+                .collect(Collectors.toMap(
+                        Map.Entry::getKey,
+                        Map.Entry::getValue,
+                        (oldVal, newVal) -> oldVal,
+                        LinkedHashMap::new
+                ));
+
+        List<Integer> list = sortedMap.keySet().stream().limit(k).toList();
+        return list.stream().mapToInt(Integer::intValue).toArray();
+    }
+}
+