JavaScript排序算法系列——快速排序

快速排序

9,     7,     1,     4,     6,      2
[1, 2]     [4]     [9,    7,    6]
[1] [2] [] [4]   [] [6] [9, 7]
[1] [2] [] [4]   [] [6] [7] [9] []

function quickSort(arr){
// 设置递归的终点
if(arr.length <= 1){
return arr;
}
// 1. 在数组中任选一个数
var midNum = arr[Math.floor(arr.length / 2)];//向下取整

// 2. 将数组分成三组
var left = [];
var middle = [];
var right = [];

// 3. 判断
for(var i = 0; i < arr.length; i++){
if(arr[i] < midNum){
left.push(arr[i]);
} else if(arr[i] == midNum){
middle.push(arr[i]);
} else if(arr[i] > midNum){
right.push(arr[i]);
}
}

// 4. 将三个分组分别用同样的方法排序并连接在一起
return quickSort(left).concat(middle, quickSort(right));
}

var arr = [1,5,7,3,12];
console.log(quickSort(arr));