chrisvest

;; chrisvest's solution to http://4clojure.com/problem/80

#(let [ntz (Integer/numberOfTrailingZeros %1)
       nlz (Integer/numberOfLeadingZeros %1)]
  (= ntz (- 31 ntz nlz)))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/77

#(->> % (group-by sort) vals (map set) (filter second) set)

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/78

(fn [f & args]
  (loop [f? (apply f args)]
    (if (fn? f?) (recur (f?)) f?)))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/73

(fn [m]
  (let [transpose (partial apply map list)
        star (fn [[[a b c] [d e f] [g h i]]] [[a e i] [c e g]])
        permute (juxt identity transpose star)
        fitness #(->> % (filter (fn [x] (apply = x))) first)]
    (->> (permute m) (map fitness) (some first) #{:x :o})))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/65

(fn [coll]
  (let [x [:a :b]
        y [:c :d]]
    (if (= (count (conj coll x x)) (count (conj coll x)))
      (if (= ((conj coll x) :a) :b) :map :set)
      (if (= (first (conj coll x y)) y) :list :vector))))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/75

(fn [x] (if (= x 1) 1
  (let [coprime (fn [y] (= 1
    (loop [dividend (max x y) ;; Euclid's GCD algorithm
         divisor (min x y)
         quotient (quot dividend divisor)
         remainder (rem dividend divisor)]
    (if (zero? remainder)
      divisor

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/60

(fn rdx
  ([f [init & coll]]
    (rdx f init coll))
  ([f init coll]
    (lazy-seq (if (empty? coll) (cons init nil)
                  (cons init (rdx f (f init (first coll)) (rest coll)))))))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/63

(fn [f coll]
  (reduce (fn [m x]
            (let [k (f x)]
              (update-in m [k] #(conj (or % []) x))))
          {} coll))

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/66

;; Using Euclid's algorithm
(fn gcd [a b]
  (loop [dividend (max a b)
         divisor (min a b)
         quotient (quot dividend divisor)
         remainder (rem dividend divisor)]
    (if (zero? remainder)
      divisor

chrisvest

;; chrisvest's solution to http://4clojure.com/problem/58

#(reduce
  (fn [f g]
    (fn [& a] (f (apply g a))))
  %&)