二路归并排序

#include <iostream>
using namespace std;

void merge(int* ptr,int first, int mid, int last)
{    
    int len = last - first + 1;
    int *temp = new int[len];
    
    
    int i = first, j = mid + 1, k = 0;
    while(i <= mid && j <= last)
    {
        if(ptr[i] <= ptr[j])
        {
            temp[k++] = ptr[i++];
        }
        else
        {
            temp[k++] = ptr[j++];
        }
    }
    while(i<=mid)
    {
        temp[k++] = ptr[i++];
    }
    while(j<=last)
    {
        temp[k++] = ptr[j++];
    }

    for( k =0;k < len; ++k)
    {
        ptr[first++] = temp[k];
    }
    delete [] temp;
}


void mergeSort(int *ptr,int first,int last)
{
    if (first < last)
    {
        int mid = (first + last)/2;
        mergeSort(ptr,first,mid);
        mergeSort(ptr,mid+1,last);
        merge(ptr,first,mid,last);
    }
}


int main()

{
    int a[] = {2,23,45,1,8,2,0};
     for(int i =0; i <= 6; ++i)
    {
        std::cout << a[i] << " ";
    }
    cout << endl;
    mergeSort(a,0,6);
    for(int i =0; i <= 6; ++i)
    {
        std::cout << a[i] << " ";
    }
    std::cout << std::endl;
    return 0;
}