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Re: Graph coloring with Scheme
From: |
Andy Wingo |
Subject: |
Re: Graph coloring with Scheme |
Date: |
Mon, 20 Jun 2016 15:09:57 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux) |
What a delight! Thank you for this elegant snippet :)
Andy
On Fri 14 Nov 2014 19:16, Jan Wedekind <address@hidden> writes:
> Hi,
> Here is an implementation [1] of Chaitin's graph coloring algorithm
> using GNU Guile and Graphviz. Any feedback and suggestions are
> welcome. Let me know if you can make the implementation more concise
> ;)
>
> Regards Jan
>
> (use-modules (srfi srfi-1)
> (srfi srfi-26))
> (define (dot graph colors)
> (apply string-append
> (append (list "graph g {")
> (map (lambda (color) (format #f " ~a [style=filled,
> fillcolor=~a];" (car color) (cdr color))) colors)
> (map (lambda (edge) (format #f " ~a -- ~a;" (car edge) (cdr
> edge))) graph)
> (list " }"))))
> (define (graphviz graph colors) (system (format #f "echo '~a' | dot -Tpng |
> display -" (dot graph colors))))
> (define (nodes graph) (delete-duplicates (append (map car graph) (map cdr
> graph))))
> (define (has-node? edge node) (or (eq? (car edge) node) (eq? (cdr edge)
> node)))
> (define (adjacent graph node) (nodes (filter (cut has-node? <> node) graph)))
> (define (remove-node graph node) (filter (lambda (edge) (not (has-node? edge
> node))) graph))
> (define (argmin fun lst)
> (let* [(vals (map fun lst))
> (minval (apply min vals))]
> (list-ref lst (- (length lst) (length (member minval vals))))))
> (define (order graph nodes)
> (if (null? nodes) '()
> (let [(target (argmin (lambda (node) (length (adjacent graph node)))
> nodes))]
> (cons target (order (remove-node graph target) (delete target
> nodes))))))
> (define (assign-colors graph nodes colors)
> (if (null? nodes) '()
> (let* [(target (car nodes))
> (coloring (assign-colors (remove-node graph target) (delete
> target nodes) colors))
> (blocked (map (cut assq-ref coloring <>) (adjacent graph
> target)))
> (available (lset-difference eq? colors blocked))]
> (cons (cons target (car available)) coloring))))
> (define (coloring graph colors) (assign-colors graph (nodes graph) colors))
> (let [(graph '((b . a) (a . c) (d . c)))] (graphviz graph (coloring graph
> '(red green blue))))
>
> [1] http://wedesoft.de/graph-coloring.html
- Re: Graph coloring with Scheme,
Andy Wingo <=