Chris Mears wrote:
> Hello Gecoders,
>
> I'd like to perform a depth first search with a specific static
> variable
> ordering. I have a matrix of integer variables and I want to label
> the
> top row first, then the left column, then the rest of the matrix in
> standard top-to-bottom, left-to-right order.
[...]
> I have managed to achieve the ordering I want, like this (with the new
> bits marked with comments):
>
> class Problem : public Space {
> IntVarArray cells;
> IntVarArray ordering; // *** added this array ***
> Problem(int n) {
> Matrix<IntVarArray> m(cells, n, n);
> // ...
> // set up constraints on cells via m
> // ...
> // *** added this block ***
> int index = 0;
> for (int c = 0 ; c < n ; c++)
> ordering[index++] = m(c,0);
> for (int r = 1 ; r < n ; r++)
> ordering[index++] = m(0,r);
You can use m.row and m.col here, like this:
branch(*this, m.row(0), ...);
branch(*this, m.col(0), ...);
> for (int r = 1 ; r < n ; r++)
> for (int c = 1 ; c < n ; c++)
> ordering[index++] = m(c,r);
> // *** search on "ordering" instead of "cells" ***
> branch(*this, cells, INT_VAR_NONE, INT_VAR_MIN);
Here you could just branch over the whole thing, as at this point the
first row and column will already be assigned and thus ignored in the
branching:
branch(*this, cells, ...);
> This seems to work. My question: is this the best way to do it? (It
> just occurred to me that maybe it could be done using Slices -- is
> that
> right?)
It's merely a matter of taste, not of efficiency, really.
Cheers,
Guido
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