Re: Q: Any ideas for this algorithm???

 James Kanze <>
Sat, 29 Sep 2007 09:12:56 -0000
On Sep 29, 10:49 am, John Harrison <>

Somebody wrote:

I have the following:

struct A
    int left;
    int top;
    int right;
    int bottom;

Thats a rectangle. I have an array of rectangles... say
ARR[nCount]... Now, I've got these elements laid out in rows
(not important how),

I would say that is important. It seems like the essense of the problem
to me.

Me too.


So it seems you have all the rects in order, which each rect
on a row having the same value for top, is that right?

I'd probably tend to use a two dimentional structure. If I
couldn't change the basic structure, something like the
following should be able to handle all cases (supposing that
"top" can be used to identify the row).

    std::map< int, int > maxPerRow ;
    for ( A* curr = begin ; curr != end ; ++ curr ) {
        int& maxBottom = maxPerRow[ curr->top ] ;
        maxBottom = std::max( maxBottom, curr->bottom ) ;
    for ( A* curr = begin ; curr != end ; ++ curr ) {
        curr->bottom = maxBottom[ curr->top ] ;

Obviously, if you can manage order, or use a two dimensional
structure, the code can be made more efficient. But anyway you
do it, you'll need two passes over each row.

James Kanze (GABI Software)
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