Clojure solution for TopCoder BinarySearchable problem

binary_searchable.clj

(ns binary-searchable)

(defn- check-pivot [sequence s index pivot]
  (cond (< pivot s) (any-pivot (drop (+ index 1) sequence) s)
        (> pivot s) (any-pivot (take index sequence) s)
        :else true))

(defn- any-pivot [sequence s]
  (if (not (empty? sequence))
    (every? #(true? %) (map-indexed (partial check-pivot sequence s) sequence))))

(defn how-many [sequence]
  (count (filter (partial any-pivot sequence) sequence)))