快速排序

快速排序使用分治法（Divide and conquer）策略来把一个串行（list）分为两个子串行（sub-lists）。

快速排序又是一种分而治之思想在排序算法上的典型应用。本质上来看，快速排序应该算是在冒泡排序基础上的递归分治法。

public class Test {

    public static void main(String[] args) {
        int[] arr = {49, 38, 65, 97, 23, 76, 1};
        quickSort(arr, 0, arr.length - 1);
        System.out.println("排序后:");
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
    }

    public static void quickSort(int[] arr, int low, int high) {
        if (low >= high) {
            return;
        }
        int index = getIndex(arr, low, high);
        quickSort(arr, low, index - 1);
        quickSort(arr, index + 1, high);
    }

    public static int getIndex(int[] arr, int low, int high) {
        int temp = arr[low];
        while (low < high) {
            while (low < high && arr[high] >= temp) {
                high--;
            }
            arr[low] = arr[high];
            while (low < high && arr[low] < temp) {
                low++;
            }
            arr[high] = arr[low];
        }
        arr[low] = temp;
        return low;
    }
}