JavaScript 快速排序法

核心思想：

1.先从数组中取出一个数作为基准数

2.定义两个空数组

3.将数组其余的每一项与基准数作比较

4.将小于等于（或大于等于）基准数的项放入准备好的一个空数组中

5.将其余的项放入另一个空数组中

6.然后通过函数递归，实现快速排序

函数封装如下：

（1）从小到大排序

        function quickSort(array) {
            if (!Array.isArray(array)) {
                return;
            }
            if (array.length <= 1) {
                return array;
            }
            var center = parseInt(array.length / 2);
            var centerNum = array.splice(center, 1);
            var left = [];
            var right = [];
            for (var i = 0; i < array.length; i++) {
                if (array[i] <= centerNum) {
                    left.push(array[i]);
                }
                else {
                    right.push(array[i]);
                }
            }
            return quickSort(left).concat(centerNum).concat(quickSort(right));
        }

（2）从大到小排序

        function quickSort(array) {
            if (!Array.isArray(array)) {
                return;
            }
            if (array.length <= 1) {
                return array;
            }
            var center = parseInt(array.length / 2);
            var centerNum = array.splice(center, 1);
            var left = [];
            var right = [];
            for (var i = 0; i < array.length; i++) {
                if (array[i] >= centerNum) {
                    left.push(array[i]);
                }
                else {
                    right.push(array[i]);
                }
            }
            return quickSort(left).concat(centerNum).concat(quickSort(right));
        }

示例：

（1）将一个数组从大到小排序

        var arr = [1, 5, 3, 6, 4, 2, 7, 4, 7, 8, 3, 6, 3, 6];
        function quickSort(array) {
            if (!Array.isArray(array)) {
                return;
            }
            if (array.length <= 1) {
                return array;
            }
            var center = parseInt(array.length / 2);
            var centerNum = array.splice(center, 1);
            var left = [];
            var right = [];
            for (var i = 0; i < array.length; i++) {
                if (array[i] >= centerNum) {
                    left.push(array[i]);
                }
                else {
                    right.push(array[i]);
                }
            }
            return quickSort(left).concat(centerNum).concat(quickSort(right));
        }
        console.log(quickSort(arr));

控制台输出：

（2）将一个数组从小到大排序

        var arr = [1, 5, 3, 6, 4, 2, 7, 4, 7, 8, 3, 6, 3, 6];
        function quickSort(array) {
            if (!Array.isArray(array)) {
                return;
            }
            if (array.length <= 1) {
                return array;
            }
            var center = parseInt(array.length / 2);
            var centerNum = array.splice(center, 1);
            var left = [];
            var right = [];
            for (var i = 0; i < array.length; i++) {
                if (array[i] <= centerNum) {
                    left.push(array[i]);
                }
                else {
                    right.push(array[i]);
                }
            }
            return quickSort(left).concat(centerNum).concat(quickSort(right));
        }
        console.log(quickSort(arr));

控制台输出：