//*************************
// Mergesort example code
// adapted from
// http://p2p.wrox.com/topic.asp?TOPIC_ID=69474
//*************************

#include <iostream>

using namespace std;

const int MAX_SIZE = 20;

void mergeSort(int numbers[],  int left, int right);
void merge(int numbers[],  int left, int mid, int right);

int main (int argc, char * argv[]) {
   int numElements = 8;
   int list [MAX_SIZE] = {9,12,16,2,1,25,4,3};
   
   cout << "before sort " << endl;
   for (int i = 0; i < numElements; i++)
      cout << list[i] << " ";
   cout << endl;
   
   
   mergeSort(list, 0, numElements - 1);
   
   cout << endl;
   cout << "after sort " << endl;
   for (int i = 0; i < numElements; i++)
      cout << list[i] << " ";
   cout << endl;
   
} 
 
 
void mergeSort(int numbers[],  int left, int right)
{
  int mid;
 
  if (right > left)
  {
    mid = (right + left) / 2;
    mergeSort(numbers,  left, mid);
    mergeSort(numbers,  mid+1, right);
 
    merge(numbers,  left, mid+1, right);
  }
}


void merge(int numbers[], int left, int mid, int right)
{
cout  << endl;
cout << "START MERGE " << "left = " << left << " mid= " <<mid<< " right = " << right << endl;
for (int i = 0; i < 8; i++)
   cout << numbers[i] << " ";
cout << endl;

  int i, left_end, num_elements, tmp_pos;
  int temp[MAX_SIZE];
  
  left_end = mid - 1;
  tmp_pos = left;
  num_elements = right - left + 1;
  
  while ((left <= left_end) && (mid <= right))
  {
    if (numbers[left] <= numbers[mid])
    {
      temp[tmp_pos] = numbers[left];
      tmp_pos = tmp_pos + 1;
      left = left +1;
    }
    else
    {
      temp[tmp_pos] = numbers[mid];
      tmp_pos = tmp_pos + 1;
      mid = mid + 1;
    }
  }
 
  while (left <= left_end)
  {
    temp[tmp_pos] = numbers[left];
    left = left + 1;
    tmp_pos = tmp_pos + 1;
  }
  while (mid <= right)
  {
    temp[tmp_pos] = numbers[mid];
    mid = mid + 1;
    tmp_pos = tmp_pos + 1;
  }
 
  for (i=0; i < num_elements; i++)
  {
    numbers[right] = temp[right];
    right = right - 1;
  }
  
/* 
cout  << endl;
cout << "END MERGE " << "left = " << left << " mid= " <<mid<< " right = " << right << endl;
for (int i = 0; i < 8; i++)
   cout << numbers[i] << " ";
cout << endl;
*/
}