sorting - shell sort

Posted 2022-12-09 小马识图

#include "stdio.h"
#include "string.h"

#define MAX_LIST 50


typedef struct _SqList 
    int data[MAX_LIST];
    int length;
SqList;

void swap( SqList* L,  unsigned index1, unsigned index2 )

    if( index1 >= L->length || index2 >= L->length ) return;

    if( index1 == index2 ) return;

    L->data[index1] = L->data[index1] ^ L->data[index2];

    L->data[index2] = L->data[index1] ^ L->data[index2];

    L->data[index1] = L->data[index1] ^ L->data[index2];


enum SHELL_SORT_METHOD  COMPLETE, BREAKDOWN ;

//the complete Shell sort implementation
//all in a do  while loop
//The rationale behind the hood is to achieve roughly sorted array
//in early rounds with a larger increment, and gradually move to
//fine granularity(eventually increment == 1 and fall back to insert sort)
//The insert sort ensures the array is sort complete
//the coarse sorting ensures less element shifting in following iterations
void ShellSortComplete( SqList* L, int divisor )

    //make sure divisor > 2
    if( divisor <= 2 )
    
        printf("Make sure divisor > 2, current value %d\\n", divisor );
        return;
    
    int increment = L->length;
    int i,j, temp;
    do
        increment = increment/divisor + 1;
        for( i = increment + 1; i < L->length; i++ ) 
        
            temp = L->data[i];
            for( j = i - increment; j > -1 && L->data[j] > temp; j -= increment )
                L->data[j+increment] = L->data[j];
            if( j + increment != i ) L->data[j+increment] = temp;
        
    while( increment > 1 );


//This is a breakdown of the complete implementation
//Single out the last iteration of do while loop which is when increment == 1
//when increment == 1, the logic is identical to the insert sort
void ShellSortBreakdown( SqList* L, int divisor )

    //make sure divisor > 2
    if( divisor <= 2 )
    
        printf("Make sure divisor > 2, current value %d\\n", divisor );
        return;
    
    int increment = L->length/divisor + 1;
    int i,j, temp;
    //if increment == 1, the while loop is omitted and Shell sort falls back to insert sort
    while( increment > 1 )
    
        for( i = increment + 1; i < L->length; i++ ) 
        
            temp = L->data[i];
            for( j = i - increment; j > -1 && L->data[j] > temp; j -= increment )
                L->data[j+increment] = L->data[j];
            if( j + increment != i ) L->data[j+increment] = temp;
        
        increment = increment/divisor + 1;
    

    //now increment == 1
    //you will be surprising to see this portion is identical to insert sort
    for( i = 1; i < L->length; i++ )
    
        temp = L->data[i];
        for( j = i - 1; j > -1 && L->data[j] > temp; j-- )
            L->data[j+1] = L->data[j];
        L->data[j+1] = temp;
    


void ShellSort( SqList* L, int divisor, SHELL_SORT_METHOD ss )

    if( ss == COMPLETE )
    
        ShellSortComplete( L, divisor );
    
    else
    
        ShellSortBreakdown( L, divisor );
    


int main()

    SqList d;
    int intarr[] = 1,10,23,48,65,31,-21,9,88,100;
    memcpy( d.data, intarr, sizeof(intarr));
    d.length = sizeof(intarr)/sizeof(int);  
    int index = 0;
    printf("Original array:\\n");
    for( ; index < d.length; index++ )
        printf(" %d", d.data[index] );
    printf("\\nShell sort...\\n");
    ShellSort( &d, 3, BREAKDOWN );
    for( index = 0; index < d.length; index++ )
        printf(" %d", d.data[index] );
    printf("\\n");
    return 0;