强制使scala函数产生“副作用”

    //
    def swap(arr:Array[Int],a:Int,b:Int)={
        val tmp = arr(a)
        arr(a)=arr(b)
        arr(b)=tmp
    }
def shuffle(arr:Array[Int])={
    val t = new Random()
    for(i <- (1 to arr.length-1).toArray.reverse)
    swap(arr,i,t.nextInt(i+1))
}