Binary search

Source code

function bsearch(a: number[], key: number): number {
    let lo = 0, hi = a.length - 1;
    while (lo <= hi) {
        const mid = Math.floor((lo + hi) / 2);
        if (a[mid] === key) return mid;
        else if (a[mid] < key) lo = mid + 1;
        else hi = mid - 1;
    }
    return -1;
}