4clojure-178-revised.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)
        rank-freqs (sort (vals (frequencies ranks)))

        flush? 
        (apply = suits) 

        straight? 
        (let [aces-high (sort ranks)
              aces-low (sort (replace {12 -1} ranks))]
          (or
            (= aces-high (take 5 (iterate inc (first aces-high))))
            (= aces-low  (take 5 (iterate inc (first aces-low))))))]
    (cond 
      (and flush? straight?) :straight-flush
      (= rank-freqs [1 4])   :four-of-a-kind
      (= rank-freqs [2 3])   :full-house
      flush?                 :flush
      straight?              :straight
      (some #{3} rank-freqs) :three-of-a-kind
      (= rank-freqs [1 2 2]) :two-pair
      (some #{2} rank-freqs) :pair
      :else                  :high-card)))