rendezvous with cassidoo #180 - Interview question of the week

rotate90.js

/* Given an n x n array, rotate it 90 degrees without making a new array.
 * rotate90([[1,2,3], [4,5,6], [7,8,9]])
 * -> [[7,4,1], [8,5,2], [9,6,3]]
 */

function rotate90(arr, isClockwise = true) {
    const size = arr.length - 1
    for (let y = 0, length = size; y <= size && length >= 0; y++, length--) {
        for (let x = y; x < length; x++) {
            let [x1, y1] = [x, y]
            let value = arr[y1][x1]
            do {
                const x2 = isClockwise ? size - y1 : y1
                const y2 = isClockwise ? x1 : size - x1
                const temp = arr[y2][x2]
                arr[y2][x2] = value
                value = temp
                x1 = x2
                y1 = y2
            } while (!(x1 === x && y1 === y))
        }
    }
    return arr
}