adjacent

gistfile1.clj

(defn two->one [[x y] [w h]]
  {:pre [(< x w) (< y h)]}
  (+ x (* y w)))

(defn one->two [i [w h]]
  {:pre [(< i (* w h))]}
  [(mod i w) (int (/ i w))])

(defn valid-space [[x y] [w h]]
  (and (<= 0 x) (<= 0 y) (< x h) (< y w)))

(defn adjacent [i [w h :as size]]
  (let [[x y] (one->two i size)]
    (for [tx (range (dec x) (+ x 2))
          ty (range (dec y) (+ y 2))]
      (when (and (valid-space [tx ty] size)
                 (not (and (= x tx) (= y ty))))
        (two->one [tx ty] size)))))

(defn adjacent-clean [i size]
  (sort (filter identity (adjacent i size))))

;; test
(let [size [3 3]]
  (assert (= '(1 3 4) (adjacent-clean 0 size)))
  (assert (= '(0 2 3 4 5) (adjacent-clean 1 size)))
  (assert (= '(3 4 7) (adjacent-clean 6 size))))