js 实现快排

function quickSort(arr){
    if(arr.length<=1) return arr;
    var pivotIndex=Math.floor(arr.length/2);
    var pivot = arr[pivotIndex];
    arr.splice(pivotIndex,1);
    var left=[],right=[];
    for(var i of arr){
        if(i<pivot)
            left.push(i);
        else
            right.push(i)
    }
    return quickSort(left).concat([pivot],quickSort(right));
}