ShellSort.cpp

#include "ShellSort.h"
#include <fstream>

using namespace std;


//-------------------------------------------------------------------------------------------------
// Function Name:     ShellSort
// Purpose:           ShellSort constructor initializes the sort table
// Parameters:        int* theValues in the unsorted list
// Returns:           none
// Pre-conditions:    none
// Post-conditions:   theList contains a pointer to the unsorted list
//-------------------------------------------------------------------------------------------------
ShellSort::ShellSort(int theCount, int* theList)
{
    this->theCount = theCount;
    this->theList = theList;
}


//-------------------------------------------------------------------------------------------------
// Function Name:     ~ShellSort
// Purpose:           ~ShellSort destructor performs house cleaning when the class is destroyed
// Parameters:        none
// Returns:           none
// Pre-conditions:    none
// Post-conditions:   none
//-------------------------------------------------------------------------------------------------
ShellSort::~ShellSort()
{
    if (theList != nullptr)
        delete[] theList;

    theCount = 0;
    theList = nullptr;
}


//-------------------------------------------------------------------------------------------------
// Function Name:     sort
// Purpose:           sort the list using the Shell Sort algorithm
// Parameters:        none
// Returns:           none
// Pre-conditions:    theList contains a valid pointer to an array of ints
// Post-conditions:   theList is sorted
//-------------------------------------------------------------------------------------------------
void ShellSort::sort()
{
    if (theCount <= 1 || theList == nullptr)
        return;

    int increment = theCount;
    do
    {
        increment = increment / 3 + 1;
        for (int insertPtr = 0; insertPtr < theCount; insertPtr++)
        {
            int tmpPtr = insertPtr;
            int tmpValue = theList[insertPtr];

            // if the current value is less than the previous swap it
            while (tmpPtr >= increment && tmpValue < theList[tmpPtr - increment])
            {
                // shift all values until either reaching the beging of the list,
                // or the values are sorted
                theList[tmpPtr] = theList[tmpPtr - increment];
                tmpPtr -= increment;
            }

            // insert the value
            theList[tmpPtr] = tmpValue;
        }

    } while (increment > 1);
}


//-------------------------------------------------------------------------------------------------
// Function Name:     saveList
// Purpose:           saves the list (sorted or unsorted) to the specified filename
// Parameters:        const char* filename is the filename to write the list to
// Returns:           true if successful, false otherwise
// Pre-conditions:    filename is not null
// Post-conditions:   none
//-------------------------------------------------------------------------------------------------
bool ShellSort::saveList(const char* filename)
{
    if (filename == nullptr)
        return false;

    ofstream outFile(filename);

    //outFile.open(filename);
    if (!outFile.good())
        return false;

    if (theList == nullptr)
    {
        theCount = 0;
        outFile << "theList was null. nothing to save." << endl;
    }

    for (int x = 0; x < theCount; x++)
        outFile << theList[x] << endl;

    outFile.close();
    return true;
}