quickSort

'use strict';

const swap = (items, firstIndex, secondIndex) => {
    var temp = items[firstIndex];
    items[firstIndex] = items[secondIndex];
    items[secondIndex] = temp;
};

const partition = (items, left, right) => {
    let index = (right + left) / 2 | 0;
    const pivot = items[index];
    let i = left;
    let j = right;
    while (i < j) { // i <= j to i < j
        while (items[i] < pivot) {
            i++;
        }
        while (items[j] > pivot) {
            j--;
        }
        if (i < j) { // i <=j to i < j
            swap(items, i, j);
            if (i === index) { // update pivot pointer
                index = j;
            } else if (j === index) {
                index = i;
            }
            i++;
            j--;
        }
    }
    return index; // return i to return index
}

const quickSort = (items, left, right) => {
    let index;
    if (items.length > 1) {
        index = partition(items, left, right);
        if (left < index - 1) {
            quickSort(items, left, index - 1);
        }
        if (index + 1 < right) { // index < right to index + 1 < right
            quickSort(items, index + 1, right); // index to index + 1
        }
    }
    return items;
};

console.log(quickSort([3, 1, 5, 2, 4], 0, 4));