Merge Sort

mergesort.cc

#include <iostream>
#define REP(i,N) for( int i = 0;i < N;i++ )
using namespace std;

//Function Declarations
void mergeSort(int numbers[], int temp[], int array_size);
void m_sort(int numbers[], int temp[], int left, int right);
void merge(int numbers[], int temp[], int left, int mid, int right);

int main(){
	
        int N; cin >> N; // Read the size of the array
        int * ar = new int[N];
        int * br = new int[N]; // Another array
      
        REP(i,N) { cin >> ar[i]; }   
      
	mergeSort(ar, br, N);

	return 0;
}


void mergeSort(int numbers[], int temp[], int array_size){
  m_sort(numbers, temp, 0, array_size - 1);
}


void m_sort(int numbers[], int temp[], int left, int right){
  int mid;

  if (right > left){
    mid = (right + left) / 2;
    m_sort(numbers, temp, left, mid);
    m_sort(numbers, temp, (mid+1), right);

    merge(numbers, temp, left, (mid+1), right);
  }
}

void merge(int numbers[], int temp[], int left, int mid, int right){
  int i, left_end, num_elements, tmp_pos;

  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 += 1;
      left += 1;
    }
    else{
      temp[tmp_pos] = numbers[mid];
      tmp_pos += 1;
      mid += 1;
    }
  }

  while (left <= left_end){
    temp[tmp_pos] = numbers[left];
    left += 1;
    tmp_pos += 1;
  }
  while (mid <= right){
    temp[tmp_pos] = numbers[mid];
    mid += 1;
    tmp_pos += 1;
  }

  //modified
  REP(i,num_elements){
    numbers[right] = temp[right];
    right--;
  }
}