快速排序 java版

java快速排序的基本版：

public class QuickSort {
    public static void quick_sort(int[] a, int p, int r) {
        if (p < r) {
            int q = partion(a, p, r);
            quick_sort(a, p, q - 1);
            quick_sort(a, q + 1, r);
        }
    }
    private static int partion(int[] a, int p, int r) {
        int x = a[r];
        int i = p - 1;
        for (int j = p; j <= r - 1; j++) {
            if (a[j] <= x) {
                i++;
                Tool.swap(a, i, j);
            }
        }
        Tool.swap(a, i + 1, r);
        return i + 1;
    }
    public static void main(String[] args) {
        int[] a = new int[] { 2, 5, 4, 5, 4, 3, 23, 2, 3, 2, 3, 2, 34, 4, 23,
                34, 5, 435, 12, 43, 5, 23, 4, 1243, 123 };
        quick_sort(a, 0, a.length - 1);
        for (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }
    }
}

下面是快速排序的随机化版本：

/**
 * 随机版本的快速排序
 *
 * @author Hercules
 *
 */
public class RandomizedQuickSort {
    public static void randomized_quick_sort(int[] a, int p, int r) {
        if (p < r) {
            int q = randomized_partion(a, p, r);
            randomized_quick_sort(a, p, q - 1);
            randomized_quick_sort(a, q + 1, r);
        }
    }
    private static int randomized_partion(int[] a, int p, int r) {
        int i = p + (int) (Math.random() * (r - p));
        Tool.swap(a, i, r);
        return partion(a, p, r);
    }
    private static int partion(int[] a, int p, int r) {
        int x = a[r];
        int i = p - 1;
        for (int j = p; j <= r - 1; j++) {
            if (a[j] <= x) {
                i++;
                Tool.swap(a, i, j);
            }
        }
        Tool.swap(a, i + 1, r);
        return i + 1;
    }
    public static void main(String[] args) {
        int[] a = new int[] { 32, 25, 34, 95, 34, 173, 23, 12, 33, 142, 53, 32,
                34, 34, 123, 34, 15, 435, 12, 43, 305, 23, 14, 1243, 123 };
        randomized_quick_sort(a, 0, a.length - 1);
        for (int i = 0; i < a.length; i++) {
            System.out.println(a[i]);
        }
    }
}

发现其他的快速排序的东西还是很好玩的