radixSort.js

// https://www.youtube.com/watch?v=XiuSW_mEn7g
// maxLen = 3 = numOfIterations
// 110, 5, 70...
// [ [110,70], [], [], [], [], [5], [], [], [], [] ]
// [ [5], [110], [], [], [], [], [], [70], [], [] ]
// [ [5,70], [110], [], [], [], [], [], [], [], [] ]
// 5, 70, 110
function createSortingArray(base = 10){
    return Array.from({length : base}, () => []);
}

function radixSort(arr){
    let max = -Infinity;
    for(const num of arr) max = Math.max(max, num); // O(n)
    let prevSortingArray = [arr];
    
    let iterations = String(max).length; // len(max digit) = d
    let i = 0;
    while(i < iterations){ // O(n * d)
        let currentSortingArray = createSortingArray(); // len = k
        const getDigit = function(num){
            return Math.floor(num / Math.pow(10,i)) % 10;
        }
        for(const subArr of prevSortingArray){
            for(const num of subArr) currentSortingArray[getDigit(num)].push(num);
        }
        i++;
        prevSortingArray = currentSortingArray;
    }

    // flatten and return
    return prevSortingArray.reduce((acc, val) => acc.concat(val), []); // O(n)
}

// range 0 - 999, all positive numbers and integers
const arr = [23,235,76,523,213,4,646,8,55,42,3,0,999,234,457,7,23];

console.log(radixSort(arr));