Data Structures (Weiss) Chapter 7: MergeSort

//

//  main.cpp

//  Data Structure TRY1

//

//  Created by zr9558 on 6/7/13.

//  Copyright (c) 2013 zr9558. All rights reserved.

//

// Data Structure C++, Weiss, P.276 MergeSort

#include<iostream>

using namespace std;

#include<vector>

#include<math.h>

/*

 a is an array oof Comparable items;

 tempArray is an array to place the merged result;

 leftPos is the left-most index of the subarray;

 rightPos is the index of the start of the second half;

 rightEnd is the right-most index of the subarray.

 */

template<typename Comparable>

void merge( vector<Comparable> &a, vector<Comparable> &tempArray, int leftPos, int rightPos, int rightEnd)

{

    int leftEnd=rightPos-1;

    int tempPos=leftPos;

    int numElements=rightEnd-leftPos+1;

    

    // Main loop

    while( leftPos<=leftEnd && rightPos<=rightEnd)

    {

        if( a[leftPos]<=a[rightPos])

            tempArray[tempPos++]=a[leftPos++];

        else

            tempArray[tempPos++]=a[rightPos++];

    }

    

    while( leftPos<=leftEnd) // Copy rest of first half

        tempArray[tempPos++]=a[leftPos++];

    

    while( rightPos<=rightEnd)

        tempArray[tempPos++]=a[rightPos++];

    

    // Copy tempArray back;

    

    for( int i=0; i<numElements; ++i, rightEnd--)

        a[rightEnd]=tempArray[rightEnd];

    

}

template<typename Comparable>

void mergeSort( vector<Comparable> &a, vector<Comparable> & tempArray, int left, int right)

{

    if( left<right)

    {

        int center=(left+right)/2;

        mergeSort(a,tempArray, left, center);

        mergeSort(a,tempArray, center+1, right);

        merge(a,tempArray, left, center+1, right);

    }

}

template<typename Comparable>

void mergeSort( vector<Comparable> &a)

{

    vector<Comparable> tempArray(a.size());

    mergeSort(a,tempArray,0,int(a.size())-1);

}

int main()

{

    vector<int> ivec;

    for( int i=0; i<30; ++i)

        ivec.push_back(rand()%100);

    

    for( int i=0; i<ivec.size(); ++i)

        cout<<ivec[i]<<" ";

    cout<<endl;

    

    

    mergeSort(ivec);

    

    for( int i=0; i<ivec.size(); ++i)

        cout<<ivec[i]<<" ";

    cout<<endl;

    

    

    

    

    return 0;

}