java 三向切分的快速排序

Posted 2021-05-08

public class Quick3Way {
    public static void sort(Comparable[] a) {
        // 将所有元素随机排序
//        List<Comparable> list = Arrays.asList(a);
//        Collections.shuffle(list);
//        a = list.toArray(new Comparable[0]);
//        StdRandom.shuffle(a);
        sort(a, 0, a.length - 1);
    }

    private static void sort(Comparable[] a, int low, int high) {
        if (high <= low) {
            return;
        }
        int lt = low, i = low + 1, gt = high;
        Comparable v = a[low];    // 切分元素
        while (i <= gt) {
            int cmp = a[i].compareTo(v);
            if (cmp < 0) {
                // a[i]<v
                exch(a, lt++, i++);
            } else if (cmp > 0) {
                // a[i]>v
                exch(a, i, gt--);
            } else {
                i++;
            }
        }
        sort(a, low, lt - 1);
        sort(a, gt + 1, high);
    }

    private static void exch(Comparable[] a, int i, int j) {
        Comparable t = a[i];
        a[i] = a[j];
        a[j] = t;
    }

    private static void show(Comparable[] a) {
        for (int i = 0; i < a.length; i++) {
            System.out.print(a[i] + " ");
        }
        System.out.println();
    }

    public static void main(String[] args) {
        Integer[] a = {1, 3, 7, 7, 0, 5, 7, 1, 0, 5, 9};
        sort(a);
        show(a);
    }
}