LeetCode #347. Top K Frequent Element

Source: Dev.to

Complexity Analysis

• Time Complexity: O(n log n) (dominated by sorting)
• Space Complexity: O(n) for the HashMap and List

Solution

class Solution {
    public int[] topKFrequent(int[] nums, int k) {
        Map map = new HashMap<>();
        for (int num : nums) {
            map.put(num, map.getOrDefault(num, 0) + 1);
        }

        List list = new ArrayList<>(map.keySet());
        list.sort((a, b) -> Integer.compare(map.get(b), map.get(a)));

        int[] result = new int[k];
        for (int i = 0; i < k; i++) {
            result[i] = list.get(i);
        }
        return result;
    }
}