希尔排序Java代码示例

import java.util.Arrays;


public class ShellSort {

    public static void sortAsc(int[] arr) {
        if (arr == null || arr.length <= 1)
            return;
        int i, j;
        int incr = arr.length;
        int count = 0; // 记录元素移动的次数
        do {
            incr = incr / 3 + 1; // 不一定非要除以3，但增量序列的最后一个增量值必须等于1
            for (i = incr; i < arr.length; i++) {
                if (arr[i] < arr[i - incr]) {
                    int t = arr[i];
                    for (j = i - incr; j >= 0 && t < arr[j]; j -= incr) {
                        arr[j + incr] = arr[j];
                        count++;
                    }
                    arr[j + incr] = t;
                    count++;
                }
            }
        } while (incr > 1);
        System.out.println("移动元素的次数：" + count);
    }

    public static void sortDesc(int[] arr) {
        if (arr == null || arr.length <= 1)
            return;
        int i, j;
        int incr = arr.length;
        do {
            incr = incr / 3 + 1;
            for (i = incr; i < arr.length; i++) {
                if (arr[i] > arr[i - incr]) {
                    int t = arr[i];
                    for (j = i - incr; j >= 0 && t > arr[j]; j -= incr)
                        arr[j + incr] = arr[j];
                    arr[j + incr] = t;
                }
            }
        } while (incr > 1);
    }

    public static void main(String[] args) {
        testCase4();
    }

    public static void testCase() {
        int[] arr = {3, 2};
        sortAsc(arr);
        System.out.println(Arrays.toString(arr));
        sortDesc(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void testCase1() {
        int[] arr = {3, 1, 2};
        sortAsc(arr);
        System.out.println(Arrays.toString(arr));
        sortDesc(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void testCase2() {
        int[] arr = {20, 11, 21, 3, 1, 25, 2, 0};
        sortAsc(arr);
        System.out.println(Arrays.toString(arr));
        sortDesc(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void testCase3() {
        int[] arr = {25, 21, 20, 18, 17, 13, 11, 9, 7, 3, 2, 1, 0};
        sortAsc(arr);
        System.out.println(Arrays.toString(arr));
    }

    public static void testCase4() {
        int[] arr = {6, 3, 3, 3, 1, 4, 2};
        sortAsc(arr);
        System.out.println(Arrays.toString(arr));
        sortDesc(arr);
        System.out.println(Arrays.toString(arr));
    }
}

对于将数组{25, 21, 20, 18, 17, 13, 11, 9, 7, 3, 2, 1, 0}按照正序排序这种极端情况，希尔排序需要移动元素29次，而直接插入排序需要移动元素90次。