STL:原地归并排序模板（InplaceMergeSort）

原理：就是在归并排序上改进，以时间复杂度换空间复杂度，利用元素反转完成排序

具体过程如下：

具体操作看代码吧，应该没什么难度，主要是reverse要反转三次

typedef int Position;

void Merge_Sort(Position, Position, int *const, Position *);
void Merge(Position, Position, int *const, Position *);
void Convert(Position, Position, Position, Position *);
void Reverse(Position, Position, Position *);
void Swap(Position *, Position, Position);

void Merge_Sort(Position Left, Position Right, int *const Inverse_Num, Position *A)
{
    if (Left < Right)
    {
        Position Mid = (Left + Right) / 2;
        Merge_Sort(Left, Mid, Inverse_Num,A);
        Merge_Sort(Mid + 1, Right, Inverse_Num,A);
        Merge(Left, Right, Inverse_Num, A);
    }
}

void Merge(Position Left, Position Right, int *const Inverse_Num, Position *A)
{
    Position Mid = (Left + Right) / 2, lpos = Left, rpos = Mid + 1, pos = Left, index = rpos;

    while (lpos <= Mid && rpos <= Right)
    {
        while (lpos < rpos && A[lpos] <= A[rpos])
            lpos++;
        index = rpos;
        while (rpos <= Right && A[rpos] < A[lpos])
            rpos++;
        Convert(lpos, index - 1, rpos - 1, A);
        lpos += rpos - index;
    }
}

void Convert(Position Left, Position Mid, Position Right, Position *A)
{
    Reverse(Left, Mid, A);
    Reverse(Mid + 1, Right, A);
    Reverse(Left, Right, A);
}

void Reverse(Position Left, Position Right, Position *A)
{
    Position i = Left, j = Right;
    while (i < j)
        Swap(A, i++, j--);
}

void Swap(Position *A, Position i, Position j)
{
    A[i] ^= A[j];
    A[j] ^= A[i];
    A[i] ^= A[j];
}

 参考：http://blog.csdn.net/acdreamers/article/details/24244643