快速排序

    function qucikSort (arr) {
        if (arr.length <= 1) {
            return arr
        }

        var num = Math.floor(arr.length / 2)
        var numVal = arr.splice(num, 1)

        var left = []
        var right = []

        for (var i = 0; i < arr.length; i++) {
            if (arr[i] < numVal) {
                left.push(arr[i])
            } else if (arr[i] > numVal) {
                right.push(arr[i])
            }
        }

        return qucikSort(left).concat(numVal, qucikSort(right))
    }