4clojure-178.clj

(fn best-hand [card-strings]
  (let [card-parser (fn [[s r]]
                      (let [suit ({\S :spade, \H :heart, 
                                   \D :diamond, \C :club} s)
                            rank (if (> (Character/digit r 10) -1)
                                   (- (Character/digit r 10) 2)
                                   ({\T 8, \J 9, 
                                     \Q 10, \K 11, \A 12} r))]
                        {:suit suit, :rank rank}))
        cards (map card-parser card-strings)
        suits (map :suit cards)
        ranks (map :rank cards)

        flush? 
        (if (= 1 (count (set suits))) :flush nil)

        straight? 
        (let [aces-high (sort ranks)
              aces-low (sort (replace {12 -1} ranks))]
               (if (or
                     (= aces-high (take 5 (iterate inc (first aces-high))))
                     (= aces-low  (take 5 (iterate inc (first aces-low)))))
                 :straight
                 nil))

        straight-flush?
        (if (and flush? straight?) :straight-flush nil)

        pair? 
        (if (some (fn [[r num]] (>= num 2)) (frequencies ranks)) 
          :pair 
          nil)

        three-of-a-kind?
        (if (some (fn [[r num]] (>= num 3)) (frequencies ranks)) 
          :three-of-a-kind
          nil)

        four-of-a-kind?
        (if (some (fn [[r num]] (= num 4)) (frequencies ranks))
          :four-of-a-kind
          nil)

        two-pair?
        (if (or 
              (some (fn [[r num]] (>= num 4)) (frequencies ranks))
              (= 2 (count (filter (fn [[r num]] (>= num 2)) 
                                  (frequencies ranks)))))
          :two-pair
          nil)
 
        full-house?
        (if (and
              (some (fn [[r num]] (= num 3)) (frequencies ranks))
              (some (fn [[r num]] (= num 2)) (frequencies ranks)))
          :full-house
          nil)
 
        possible-hands 
        (remove nil? [straight-flush? four-of-a-kind? full-house? flush?
                      straight? three-of-a-kind? two-pair? pair?])]
    (if-not (empty? possible-hands)
      (first possible-hands)
      :high-card)))