C++实现归并排序

#include<iostream>
#include<algorithm>
using namespace std;
 
void merge(int *data,int start,int end,int *result) 
{
  int left_length = (end - start + 1) / 2 + 1;  
  int left_index = start;
  int right_index = start + left_length;
  int result_index = start;
  while(left_index<start + left_length && right_index <end + 1) //store data into new array
  {
    if(data[left_index] <= data[right_index])
      result[result_index++] = data[left_index++];
    else
      result[result_index++] = data[right_index++];
  }
  while(left_index < start + left_length)
    result[result_index++] = data[left_index++];
  while(right_index <end+1)
    result[result_index++] = data[right_index++];
}
 
void merge_sort(int *data,int start,int end,int *result)
{
  if(1 == end - start)  //last only two elements
  {
    if(data[start] > data[end])
    {
      int temp = data[start];
      data[start] = data[end];
      data[end] = temp;
    }
    return;
  }
  else if (end == start)
    return; //last one element then there is no need to sort;
  else{
    //continue to divide the interval
    merge_sort(data, start, (end - start + 1) / 2 + start, result);
    merge_sort(data, (end - start + 1) / 2 + start + 1, end, result);
    //start to merge sorted data
    merge(data, start, end, result);
    for (int i = start; i <= end;++i)
    {
      data[i] = result[i];
    }
  }
 
}
//example
int main()
{
  int data[] = {5,3,6,7,3,2,7,9,8,6,34,32,5,4,43,12,37};
  int length = 17;
  int result[length];
  cout << "before sorted:"<<'\n';
  for (int i = 0; i < length;i++)
    cout << data[i]<<' ';
  cout << '\n'
     << "after sorted:"<<'\n';
  merge_sort(data, 0, length - 1, result);
  for (int i = 0; i < length;i++)
    cout << result[i]<<' ';
  return 0;
}