function quickSort(arr){
if(arr.length == 0){
return [];
}
var left = [];
var right = [];
var selectItem = arr[0];
for(var i = 1; i < arr.length; i++){
if(arr[i] < selectItem){
left.push(arr[i]);
} else{
right.push(arr[i]);
}
}
return quickSort(left).concat(selectItem, quickSort(right));
}