Why does it call Shell Sort? This time it's name has little to do with the method it uses. In fact , it's alse call Decreasing incremental sorting algorithm (递减增量排序算法)
It's because of Donald Shell, who invented this method:
divide List into servral column (first column = length/2)
but each time column get smaller, until column =1 (when column =1 , it become a real insert sort)
each insert sort , it's elements include each column instead of the whole List .
It's main feature : compare more but move less.
#include <stdio.h>
#include "type.h"void ShellSort(SqList *L)
{
int increase_step = 2;
//div List into several column , and each column use insert sort
for(int column = L->length/increase_step; column >0; column=column/increase_step)
{
//insert sort of each column
for( int line = column; line < L->length; line++)
{
int com = L->data[line];
int j= line - column;
//in a step of column_num
for( ; com < L->data[j] && j>=0 ; j-=column)
{
L->data[j+column]=L->data[j];
}
L->data[j+column] = com;
}
//for clear watch a List , output the List in column
for(int i = 0; i< L->length; i++)
{
if(0== i%column)
printf("\n");
printf("%d ", L->data[i]);
}
printf("\n\n");
}
}
void printContent(SqList *L)
{
for(int i = 0; i< L->length; i++)
{
printf("%d \t",L->data[i] );
}
}
int main(void)
{
SqList l ;
l.data={17,16,15,14,13,12,11,10,9,8,7,6,5,4,3,2,1};
l.length = 17;
printContent(&l);
printf("\n");
ShellSort(&l);
printContent(&l);
printf("\n");
return 0;
}
17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 (first , original)
(column set to 17/2 = 8, the following is the first sort result of each column. Note that each column is in order now)
1 8 7 6 5 4 3 2
9 16 15 14 13 12 11 10
17
(column set to 8/2 = 4, the following is the first sort result of each column. Note that each column is in order now, again)
1 4 3 2
5 8 7 6
9 12 11 10
13 16 15 14
17
(column set to 4/2 = 2, the following is the first sort result of each column. Note that each column is in order now)
1 2
3 4
5 6
7 8
9 10
11 12
13 14
15 16
17
(in the end, this is just a insert sort)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
(final result)
(column set to 17/2 = 8, the following is the first sort result of each column. Note that each column is in order now)
1 8 7 6 5 4 3 2
9 16 15 14 13 12 11 10
17
(column set to 8/2 = 4, the following is the first sort result of each column. Note that each column is in order now, again)
1 4 3 2
5 8 7 6
9 12 11 10
13 16 15 14
17
(column set to 4/2 = 2, the following is the first sort result of each column. Note that each column is in order now)
1 2
3 4
5 6
7 8
9 10
11 12
13 14
15 16
17
(in the end, this is just a insert sort)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
(final result)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
the most difficult point to understand is about increase_step , it set to length/2 at the first time . But it has some way to improve . refer to this.