Top K Frequent Elements

Author: forest000014

top-k-frequent-elements/forest000014.java

@@ -0,0 +1,52 @@
+/*
+Runtime: 10 ms(Beats: 95.83 %)
+Time Complexity: O(nlogn)
+- map에 item 추가 : O(n)
+- items 배열 정렬 : O(nlogn)
+- result 배열에 원소 추가 : O(n)
+
+Memory: 49.50 MB(Beats: 6.84 %)
+Space Complexity: O(n)
+- map : O(n)
+- items : O(n)
+- result : O(n)
+*/
+
+class Solution {
+    class Item {
+        int val;
+        int cnt;
+
+        public Item(int val, int cnt) {
+            this.val = val;
+            this.cnt = cnt;
+        }
+
+        public void plusOne() {
+            this.cnt += 1;
+        }
+    }
+
+    public int[] topKFrequent(int[] nums, int k) {
+        Map<Integer, Item> map = new HashMap<>();
+        for (int num : nums) {
+            Item item = map.get(num);
+            if (item == null) {
+                item = new Item(num, 1);
+                map.put(num, item);
+            } else {
+                item.plusOne();
+            }
+        }
+
+        ArrayList<Item> items = new ArrayList<>(map.values());
+        Collections.sort(items, (item1, item2) -> Integer.compare(item2.cnt, item1.cnt));
+
+        int[] result = new int[k];
+        for (int i = 0; i < k; i++) {
+            result[i] = items.get(i).val;
+        }
+
+        return result;
+    }
+}