归并排序(无哨兵实现)

void Merge(int *a, int ileft, int imid, int iright) //辅助函数
{
    int n1 = imid - ileft + 1; 
    int n2 = iright - imid; 

    int *Larray = new int[n1];
    int *Rarray = new int[n2];

    //分解
    for(int i = 0; i <= n1 - 1; i++)
    {
        Larray[i] = a[ileft+i];
    }
    for(int j = 0; j <= n2 - 1; j++)
    {
        Rarray[j] = a[imid+1+j];
    }

    //合并
    int i = 0, j =0;
    for(int k = ileft; k <= iright; k++)
    {
        if(i==n1) //Larray中已无元素(i越界)
        {
            a[k] = Rarray[j];
            j++;
        }
        else if(j==n2) //Rarray中已无元素(j越界)
        {
            a[k] = Larray[i];
            i++;
        }
        else
        {
            if(Larray[i]<=Rarray[j])
            {
                a[k] = Larray[i];
                i++;
            }
            else
            {
                a[k] = Rarray[j];
                j++;
            }
        }
    }

    delete []Larray;
    delete []Rarray;
}

void MergeSort(int *a, int ileft, int iright)  //接口
{
    if(ileft < iright)
    {
        int imid = (ileft + iright) / 2;
        MergeSort(a, ileft, imid);
        MergeSort(a, imid+1, iright);
        Merge(a, ileft, imid, iright);
    }
}