347_top_k_frequent_elements.js

/**
 * https://leetcode.com/problems/top-k-frequent-elements/
 * 
 * @param {number[]} nums
 * @param {number} k
 * @return {number[]}
 */

const zip = (l1, l2) => l1.map((e, i) => [e, l2[i]])
const zipWith = (l1, l2, fn) => zip(l1, l2).map(([a, b]) => fn(a, b))
const toArray = obj => zipWith(Object.keys(obj), Object.values(obj), (key, value) => ({ key, value }))

const reducer = (counts, num) => {
    counts[num] = counts[num] ? counts[num] + 1 : 1
    return counts
}

const getCounts = nums => nums.reduce(reducer, {})

var topKFrequent = function(nums, k) {
    return toArray(getCounts(nums))
        .sort((a, b) => b.value - a.value)
        .slice(0, k)
        .map(e => parseInt(e.key))
};