[JAVA data structure] Hill sorting/shrinking incremental method

        Pre-content: [JAVA] Direct insertion sort_HY_PIGIE's Blog-CSDN Blog

        Hill sorting is to divide an array into multiple groups and sort within each group. Every time a sort is performed, the elements in the group will increase and the number of groups will decrease.

Insertion sort directly         within a group

        The number of groups is reduced by /2

        For example, an array contains 6 elements. Initially, two elements can be used as a group, and the number of groups gap is: 8/2=4 groups.

direct insertion sort          in each group

         The number of elements in the group is increased, and the number of groups sorted for the second time can be gap: 4/2=2;

        Sorting process:

        Pay attention to the observation that the sorting in the group is carried out alternately, instead of arranging the elements in a whole group in an orderly manner at one time.

         After sorting:

         The third sorting, the number of groups gap: 2/2=1

        We can find that after each sorting, the array as a whole gradually tends to be in order. At this time, the entire array is used as a group to perform overall sorting.

         After sorting it is:

         On the code!

import java.util.Arrays;

public class Test {
    public static void shell(int[] array,int gap){
        //可以思考一下为什么i从gap开始呢？
        //i从gap开始，表示的就是第一组的第二个元素
        //gap其实是每一组相邻元素在整体数组内下标的联系
        //gap是两个相邻元素的下标的差额
        //每个组内进行插入排序
        for(int i = gap; i < array.length; i++){
            //i表示每一组的开头
            //i++表示的是每一组的排序交替进行
            //即A组进行一次插入排序后，B组进行一次，然后A在进行一次，循环往复
            int j = i - gap;
            int tmp = array[i];
            for(; j >= 0; j -= gap){
                if(tmp < array[j]){
                    array[j+gap] = array[j];
                }else{
                    break;
                }
            }
            array[j+gap] = tmp;
        }
    }
    public static void shellSort(int[] array){
        int gap = array.length;
        while(gap > 1){
            //最后一次排序是整个数组为一组的时候
            gap /= 2;//组数每一次都/2
            shell(array,gap);
        }
    }
    public static void main(String[] args) {
        int[] array = {12,89,2,4,61,50};
        shellSort(array);
        System.out.println(Arrays.toString(array));
    }
}