From: Ramakrishnan Muthukrishnan Date: Mon, 7 Jan 2013 17:04:08 +0000 (+0530) Subject: Solution to 4.44. A bit too verbose. Can be improved by better X-Git-Url: https://git.rkrishnan.org/Site/Content/Exhibitors/%22news.html/%22file:/htmlfontify-example.html?a=commitdiff_plain;h=c3062a9e8691e9c067b69ec24a728c746520b310;p=sicp.git Solution to 4.44. A bit too verbose. Can be improved by better board representation. --- diff --git a/src/sicp/ex4_44.rkt b/src/sicp/ex4_44.rkt new file mode 100644 index 0000000..5672d7e --- /dev/null +++ b/src/sicp/ex4_44.rkt @@ -0,0 +1,81 @@ +#lang racket + +(require "amb-eli.rkt") +(require "distinct.rkt") + +(define (queens) + (let ([q1r (amb 1 2 3 4 5 6 7 8)] + [q1c (amb 1 2 3 4 5 6 7 8)] + [q2r (amb 1 2 3 4 5 6 7 8)] + [q2c (amb 1 2 3 4 5 6 7 8)]) + (assert (distinct? (list q1r q2r))) + (assert (distinct? (list q1c q2c))) + (assert (not (diagonal? (list q1r q1c) (list q2r q2c)))) + (let ([q3r (amb 1 2 3 4 5 6 7 8)] + [q3c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r)]) + (assert (distinct? (list q3r qr)))) + (for ([qc (list q1c q2c)]) + (assert (distinct? (list q3c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c))]) + (assert (not (diagonal? (list q3r q3c) q)))) + (let ([q4r (amb 1 2 3 4 5 6 7 8)] + [q4c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r q3r)]) + (assert (distinct? (list q4r qr)))) + (for ([qc (list q1c q2c q3c)]) + (assert (distinct? (list q4c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c) (list q3r q3c))]) + (assert (not (diagonal? (list q4r q4c) q)))) + (let ([q5r (amb 1 2 3 4 5 6 7 8)] + [q5c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r q3r q4r)]) + (assert (distinct? (list q5r qr)))) + (for ([qc (list q1c q2c q3c q4c)]) + (assert (distinct? (list q5c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c) (list q3r q3c) (list q4r q4c))]) + (assert (not (diagonal? (list q5r q5c) q)))) + (let ([q6r (amb 1 2 3 4 5 6 7 8)] + [q6c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r q3r q4r q5r)]) + (assert (distinct? (list q6r qr)))) + (for ([qc (list q1c q2c q3c q4c q5c)]) + (assert (distinct? (list q6c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c) (list q3r q3c) (list q4r q4c) (list q5r q5c))]) + (assert (not (diagonal? (list q6r q6c) q)))) + (let ([q7r (amb 1 2 3 4 5 6 7 8)] + [q7c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r q3r q4r q5r q6r)]) + (assert (distinct? (list q7r qr)))) + (for ([qc (list q1c q2c q3c q4c q5c q6c)]) + (assert (distinct? (list q7c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c) (list q3r q3c) (list q4r q4c) (list q5r q5c) (list q6r q6c))]) + (assert (not (diagonal? (list q7r q7c) q)))) + (let ([q8r (amb 1 2 3 4 5 6 7 8)] + [q8c (amb 1 2 3 4 5 6 7 8)]) + (for ([qr (list q1r q2r q3r q4r q5r q6r q7r)]) + (assert (distinct? (list q8r qr)))) + (for ([qc (list q1c q2c q3c q4c q5c q6c q7c)]) + (assert (distinct? (list q8c qc)))) + (for ([q (list (list q1r q1c) (list q2r q2c) (list q3r q3c) (list q4r q4c) (list q5r q5c) (list q6r q6c) (list q7r q7c))]) + (assert (not (diagonal? (list q8r q8c) q)))) + (list (list 'q1 q1r q1c) + (list 'q2 q2r q2c) + (list 'q3 q3r q3c) + (list 'q4 q4r q4c) + (list 'q5 q5r q5c) + (list 'q6 q6r q6c) + (list 'q7 q7r q7c) + (list 'q8 q8r q8c)))))))))) + +(define (diagonal? p1 p2) + (let ([x1 (first p1)] + [y1 (second p1)] + [x2 (first p2)] + [y2 (second p2)]) + (= (abs (- x1 x2)) + (abs (- y1 y2))))) + +(queens) + +;; '((q1 1 1) (q2 2 5) (q3 3 8) (q4 4 6) (q5 5 3) (q6 6 7) (q7 7 2) (q8 8 4)) \ No newline at end of file