fronx-4clojure-solution127.clj

;; fronx's solution to Love Triangle
;; https://4clojure.com/problem/127

(fn [field]
  (let [
        bit-max  (fn [int]
                   (loop [n 1 i 0]
                     (if (>= int n)
                         (recur (* 2 n) (inc i))
                         i)))
    max-bit-max  (fn [ints] (bit-max (apply max ints)))
      flip-down  #(reverse %)
     flip-right  (fn [triangle]
                   (map #(bit-shift-left % (- (max-bit-max triangle) (bit-max %)))
                        triangle))
        tri-at?  (fn [triangle x y field]
                   (if (>= (count field) (+ y (count triangle)))
                       (let [triangle (vec (map #(bit-shift-left % x) triangle))
                             matchfield (subvec field y)]
                         (every? true?
                           (map (fn [tri x]
                                  (= tri (bit-and tri x)))
                                triangle
                                matchfield)))))
      bit-count  (fn [ints] (reduce + (map #(Integer/bitCount %) ints)))
          wedge  (fn [size]
                    (take size ((fn wedge
                                 ([] (wedge [1]))
                                 ([prev] (lazy-cat prev
                                   (wedge [(+ 1 (bit-shift-left (peek prev) 1))])
                               ))))))
            fir  (fn [size]
                   (map #(bit-or % (bit-shift-left %2 size))
                        (flip-right (wedge size))
                        (concat [0] (wedge (dec size)))))
    play-button  (fn [size]
                  (concat (wedge size)
                          (flip-down (wedge (dec size)))))
      triangles  (fn [size]
                   (let [a (wedge size)
                         b (flip-right a)
                         c (flip-down a)
                         d (flip-down b)
                         e (fir size)
                         f (flip-down e)
                         g (play-button size)
                         h (flip-right g)]
                     (set [a b c d e f g h])))
          x-max  (max-bit-max field)]
  (loop [size 2 biggest 0]
    (let [found (for [tri (triangles size)
                        x (range 0 x-max)
                        y (range 0 (inc (- (count field) (count tri))))
                        :when (tri-at? tri x y field)]
                  (bit-count tri))]
      (if (or (empty? found)
              (<= (apply max found) biggest))
          (if (> biggest 0) biggest)
          (recur (inc size) (apply max found)))))))

@nisc I invited more lazy cats. Still waiting for them to respond.