squaro.clj

(ns logic-puzzle.core
  (:refer-clojure :exclude [==])
  (:require [clojure.core.logic :refer :all]))

(defn squaro [q]
  (let [colors [:red :green :blue :yellow]]
    (fresh [a1 a2 a3 a4
            b1 b2 b3 b4]
      (all
       (permuteo colors [a1 a2 a3 a4])
       (permuteo colors [b1 b2 b3 b4])
       (!= a1 b1)
       (!= a2 b2)
       (!= a3 b3)
       (!= a4 b4)
       (== q [a1 a2 a3 a4 b1 b2 b3 b4])))))

(run 1 [q]
  (squaro q))
;; => ([:red :green :blue :yellow :green :blue :yellow :red])

(count (run* [q] (squaro q)))
;; => 216

Each of the squares of two rows of squares (2x4) is coloured in one of 4 di�erent colours red, yellow, green and blue. Find the number of ways of colouring the two rows so that each row has 4 di�erent colours and no two adjacent squares are of the same colour. (Two squares are adjacent if they share a common side.)