https://leetcode.com/problems/top-k-frequent-elements/

topKFrequent.js

/**
 * @param {number[]} nums
 * @param {number} k
 * @return {number[]}
 */
var topKFrequent = function(nums, k) {
    
    const counter = new Map();
    nums.forEach((n) => {
        if(!counter.has(n)) counter.set(n, 1);
        else counter.set(n, counter.get(n) + 1);
    });
    
    const counts = new Array(nums.length+1).fill(0).map(() => []);
    for(let [num, count] of counter) counts[count].push(num);
    
    const result = [];
    for(let i=counts.length-1; i>=0 && result.length < k; i--){
        result.push(...counts[i]);
    }
    return result;
};