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

From:
James Kanze <james.kanze@gmail.com>
Newsgroups:
comp.lang.c++
Date:
Sat, 29 Sep 2007 09:12:56 -0000
Message-ID:
On Sep 29, 10:49 am, John Harrison <john_androni...@hotmail.com>
wrote:

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) email:james.kanze@gmail.com
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