function quickSort(arr){

    if(arr.length<=1){return arr;}
    var pivotIndex=Math.floor(arr.length/2);
    var pivot=arr.splice(pivotIndex,1)[0];
    //定义
    var left=[];
    var right=[];
    //小的放left，大的放right
    for(var i=0;i<arr.length;i++){
        if(arr[i]<=pivot){
            left.push(arr[i]);
        }else{
            right.push(arr[i]);
        }
    }
    //递归
    //从小到大
    return quickSort(left).concat([pivot],quickSort(right)); 
   //大到小  
   //return quickSort(right).concat([pivot],quickSort(left)); 
}