递归实现归并排序

/*************************************************************************
    > File Name: merge_sort.cpp
    > Author:
    > Description: 
    > Created Time: Sun 26 Jul 2015 10:15:24 AM HKT
 ************************************************************************/

#include<iostream>
using namespace std;

void merge(int a[],int tmp[],int lPos,int rPos,int rEnd)
{
    int numElements=rEnd-lPos+1;// 计算元素个数
    int lEnd=rPos-1;
    int tmpPos=lPos;
    while(lPos<=lEnd && rPos<=rEnd)
    {
        if(a[lPos]<=a[rPos])
            tmp[tmpPos++]=a[lPos++];
        else
            tmp[tmpPos++]=a[rPos++];
    }

    //到这里左端或右端可能还有剩余元素
    while(lPos<=lEnd)
        tmp[tmpPos++]=a[lPos++];
    while(rPos<=rEnd)
        tmp[tmpPos++]=a[rPos++];

    for(int i=0;i<numElements;i++)
    {
        a[rEnd]=tmp[rEnd--];
    }
}

void msort(int a[],int tmp[],int low,int high)
{
    if(low>=high)
        return;
    int middle=(low+high)/2;
    msort(a,tmp,low,middle);
    msort(a,tmp,middle+1,high);
    merge(a,tmp,low,middle+1,high);
}

void merge_sort(int a[],int len)
{
    int *tmp=new int[len];
    if(tmp !=NULL)
    {
        msort(a,tmp,0,len-1);
        delete []tmp;
    }
}
int main()
{
    int a[]={1,4,7,6,3,8,2,5};
    merge_sort(a,8);
    for(int i=0;i<8;i++)
    {
        cout<<a[i]<<" ";
    }
    cout<<endl;

    return 0;
}