程序代码：

void mergeImproved( vector<Comparable> &a )
{
    int size = a.size();
    vector<Comparable> b( size );  // 唯一的临时数组
    int maxLayer = 1;
    for ( int items = 2; items < size; items *= 2, ++maxLayer );

    // for each layer, perform merge sort.
    for ( int curLayer = 0, items = 0; curLayer < maxLayer; ++curLayer )
    {
        items = int( pow( double( 2 ), double( curLayer ) ) );//功能：pow(x,y)返回x的y次幂

        // decide which array of a and b is input or output
        vector<Comparable> &in = ( curLayer % 2 == 0 ) ? a : b;
        vector<Comparable> &out = ( curLayer % 2 == 0 ) ? b : a;
        
        // for each left and right sub arrays on the block
        for ( int index = 0; index < size; index += ( 2 * items ) ) 
        {

            // fix the left array's first and last indices
            int first1 = index;
            int last1 = ( first1 + items - 1 < size - 1 ) ? first1 + items - 1 : size - 1;

            // fix the right array's first and last indices
            int first2 = ( last1 + 1 < size - 1 ) ? last1 + 1 : size - 1;
            int last2 = (first2 + items - 1 < size - 1 ) ? first2 + items - 1 : size - 1;

            // now merge them in one block
            int outIx = first1;
            for ( ; first1 <= last1 && first2 <= last2; ++outIx )
                out[outIx] = ( in[first1] < in[first2] ) ? in[first1++] : in[first2++];

            for ( ; first1 <= last1; ++first1, ++outIx )
                out[outIx] = in[first1];

            for ( ; first2 <= last2; ++first2, ++outIx )
                out[outIx] = in[first2];
        }
    }

    // in case the sort items are in the temporary array
    if ( maxLayer % 2 == 1 )
        a = b; // copy them back to the original
}

  int first2 = ( last1 + 1 < size - 1 ) ? last1 + 1 : size - 1;

  int first2 = ( last1 + 1 < size - 1 ) ? last1 + 1 : size;