TopKFreq.java

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

class Solution {
    public int[] topKFrequent(int[] nums, int k){
    Map<Integer, Integer> count = new HashMap<>();

    for(int n : nums){
        count.put(n, count.getOrDefault(n, 0) + 1);
    }

    List<Integer>[] freq = new List[nums.length + 1];
    for(int i = 0; i < freq.length; i++){
        freq[i] = new ArrayList<>;
    }

    for(Map.Entry<Integer, Integer> entry : count.entrySet()){
        freq[entry.getValue()].add(entry.getKey());
    }

    int[] res = new int[k];
    int index = 0;
    for(int i = freq.length - 1; i > 0 && index < k; i--){
        for(int n : freq[i]) {
            res[index++] = n;
            if(index == k){
                return res;
            }
        }
    }
        return res;
    }
}