算法——希尔排序

 希尔排序是插入排序的进化版，在进行比交换位置时以增量进行交换或移动；通过比较相距一定间隔的元素来工作；各趟比较所用的距离随着算法的进行而减小，直到只比相邻元素的最后一趟排序为止，因此有时也叫缩减增量排序

  直接上代码吧（可能并不是最好的例子）：

 public void shellSort(){
        int[] a = {81,94,11,96,12,35,17,95,28,58,41,75,15};
        System.out.println(Arrays.toString(a));
        int j;
        for (int gap = a.length/2; gap > 0 ; gap /= 2) {
            for (int i = gap; i < a.length; i++) {
                int tmp = a[i];
                for (j = i; j >= gap && tmp < a[j-gap] ; j -= gap) {
                    a[j] = a[j-gap];
                }
                a[j] = tmp;
            }
        }
        System.out.println(Arrays.toString(a));
    }

 以gap=3为例，结合代码：

public void shellSort(){
        int[] a = {15, 94, 11, 58, 12, 35, 17, 95, 28, 96, 41, 75, 81};//gap=3之前的数组
        System.out.println(Arrays.toString(a));
        int j;
        for (int gap = a.length/2; gap > 0 ; gap /= 2) {
            for (int i = gap; i < a.length; i++) {
                int tmp = a[i];//tmp
                for (j = i; j >= gap && tmp < a[j-gap] ; j -= gap) {
                    a[j] = a[j-gap];
                   //15, 94, 11, 58, 94, 35, 17, 95, 28, 96, 41, 75, 81
                  //15, 12, 11, 58, 94, 35, 58, 95, 28, 96, 41, 75, 81
                   //15, 12, 11, 17, 94, 35, 58, 95, 35, 96, 41, 75, 81
                   //15, 12, 11, 17, 94, 28, 58, 95, 35, 96, 95, 75, 81
                    //15, 12, 11, 17, 94, 28, 58, 94, 35, 96, 95, 75, 81
                     //15, 12, 11, 17, 41, 28, 58, 94, 35, 96, 95, 75, 96
                }
                a[j] = tmp;
            }
　　　　　　//gap=3之后的数组：[15, 12, 11, 17, 41, 28, 58, 94, 35, 81, 95, 75, 96]
        }
        System.out.println(Arrays.toString(a));
    } 

希尔排序与插入排序不同的是：希尔排序是增量式的不想普通的插入排序一个一个的往前比较，而是按增量进行大间距的移动或交换