排序之 快速排序

import java.util.Arrays;

public class MySort {

    public static void quickSort(int[] a) {
        qSort(a, 0, a.length - 1);
    }

    private static void qSort(int[] a, int p, int r) {
        if (p < r) {
            int q = partition(a, p, r);
            qSort(a, p, q - 1);
            qSort(a, q + 1, r);
        }
    }

    private static int partition(int[] a, int p, int r) {
        int x = a[r];
        int i = p - 1;
        int j = p;
        for (j = p; j < r; j++) {
            if (a[j] <= x) {
                i++;
                swap(a, i, j);
            }
        }
        swap(a, i + 1, r);

        return i + 1;
    }

    private static void swap(int[] a, int i, int j) {
        if (i != j) {
            int tmp = a[i];
            a[i] = a[j];
            a[j] = tmp;
        }

    }

    public static void main(String[] args) {
        int[] a = { 2, 8, 7, 1, 3, 5, 6, 4 };
        System.out.println(Arrays.toString(a));
        quickSort(a);
        System.out.println(Arrays.toString(a));

    }

}