Quick Select Algorithm for finding Kth Max Element

QuickSelect.js

function partition(a, lo, hi) {
    /* 
    //Improve partition choice for the worst case 
    const randomIndex = Math.floor(Math.random() * (hi - lo + 1)) + lo;
    swap(a, lo, randomIndex);  // Move the random pivot to the start
     */
    let i = lo;
    let j = hi + 1;
    let P = a[lo];

    while (true) {
        do {
            i++;
        } while (a[i] < P);

        do {
            j--;
        } while (a[j] > P);

        if (i >= j) break;
        swap(a, i, j);
    }
    swap(a, lo, j);
    return j;
}

const swap = (a, i, j) => ([a[i], a[j]] = [a[j], a[i]]);

function findKthLargest(nums, k) {
    k = nums.length - k;
    let lo = 0;
    let hi = nums.length - 1;

    while (lo <= hi) {
        const j = partition(nums, lo, hi);
        if (j === k) return nums[k];
        else if (j < k) lo = j + 1;
        else hi = j - 1;
    }
}