4clojure_178.clj

(fn best-hand
  [hand]
  (let [ranks (map second hand)
        suits (map first hand)
        rank-freqs (sort (vals (frequencies ranks)))]
    (letfn [(flush? [hand]
              (apply = suits))
            (straight? [hand]
              (let [straight-hands (set (map set (partition 5 1 [\A \2 \3 \4 \5
                                                                 \6 \7 \8 \9 \T
                                                                 \J \Q \K \A])))]
                (straight-hands (set ranks))))]
      (cond (= [2 3] rank-freqs) :full-house
            (= [1 2 2] rank-freqs) :two-pair
            (= [1 4] rank-freqs) :four-of-a-kind 
            (= [1 1 3] rank-freqs) :three-of-a-kind
            (= [1 1 1 2] rank-freqs) :pair
            (and (straight? hand) (flush? hand)) :straight-flush
            (flush? hand) :flush
            (straight? hand) :straight
            :else :high-card))))