Thread: Learning Merge Sort Technique

I am beginning to learn the merge sort technique, i will be applying the concepts to a recursive function, but currently i have a linear function that takes in two arrays and merges them. is my interpretation correct, the program works fine no errors, correct output, but have i used too many steps, just making sure i have it correct. thanks.

btw, ap header files are used, same datatypes can be found in iostream, vector....etc....you know.....

Code:

#include <iostream>
#include <iomanip>
#include <dice.h>
#include <apvector.h> 
using namespace std;

const int SIZE = 200;

void fillArray (apvector<int> &temp);
void screenOutput (const apvector<int> &temp);
void swap (int &a, int &b);
void selectionSort (apvector<int> &list);
void mergeSort(apvector<int> &listA, 
               apvector<int> &listB, 
               apvector<int> &listC);

main()
{
      apvector<int> listA(SIZE+1); 
      apvector<int> listB(SIZE+1);
      apvector<int> listC((2*SIZE)+1);
      fillArray (listA);
      fillArray (listB);
      selectionSort (listA);
      selectionSort (listB);
      mergeSort (listA, listB, listC);
      screenOutput (listC);
      system("pause");
      return 0;
}

void fillArray (apvector<int> &temp)
{
      int  size; 
      cout << "How many numbers to you wish to generate? ";
      cin >> temp[0];
      cout << "Largest integer to generate? ";
      cin >> size;
      cout << endl;
      dice die(size);      // allocate dice object
      for (int loop=1; loop<=temp[0]; loop++)
            temp[loop] = die.roll();
} 

void screenOutput (const apvector<int> &temp)
{
      cout << setiosflags (ios::right) << endl;
      for (int loop=1; loop<=temp[0]; loop++)
      {
            cout << setw(4) << temp[loop];
            if (loop % 20 == 0) cout << endl;
      }
      cout << endl;
} 

void swap (int &a, int &b)
{
      int temp = a;
      a = b;
      b = temp;
} 

void selectionSort (apvector<int> &list)
{
   int flag;
   
   for (int outer = 1; outer < list[0]; outer++)
   {
      flag = outer;
      for (int inner = outer + 1; inner <= list[0]; inner++)
      {
         if (list[inner] < list[flag])
         {
            flag = inner;
         }
      }
      swap(list[outer], list[flag]);
   }
}

void mergeSort(apvector<int> &listA, 
               apvector<int> &listB, 
               apvector<int> &listC)
{
   listC[0] = listA[0] + listB[0];
   int indexA = 1, indexB = 1, indexC = 1;
   while (indexA <= listA[0] && indexB <= listB[0])
   {
      if (listA[indexA] < listB[indexB])
      {   
         listC[indexC] = listA[indexA];
         indexA++;
         indexC++;
      }
      if (listB[indexB] <= listA[indexA])
      {
         listC[indexC] = listB[indexB];
         indexB++;
         indexC++;
      }
   }
   if (indexA > listA[0])
      for (indexB; indexB <= listB[0]; indexB++)
      {
         listC[indexC] = listB[indexB];
         indexC++;
      }
   else if (indexB > listB[0])
      for (indexA; indexA <= listA[0]; indexA++)
      {
         listC[indexC] = listA[indexA];
         indexC++;
      }
}