数组旋转k步

　　时间复杂度O(n^2) 空间复杂度O(1)

const rorateKstep = (arr = [1,2,3,4,5,6,7],step = 3) => {
    const length = arr.length
    for(let i = 0; i < 3;i++){
        arr.unshift(arr[arr.length - 1])
        arr.length = length
    }
    return arr
}

　　时间复杂度O(1) 空间复杂度O(n)

const rorateKstep = (arr = [1,2,3,4,5,6,7],step = 3) => {
    const length = arr.length
    arr = arr.slice(-step).concat(arr);
    arr.length = length
    return arr
}