jneira

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

(fn [f c] (reduce (fn [m n] (merge-with into m {(f n) [n]})) {} c))

jneira

;; jneira's solution to http://4clojure.com/problem/67

(fn primes [n]
  (letfn
      [(next-prime
	[prs nxt]
	(if (empty? (filter #(= 0 (mod nxt %)) prs))
	  (conj prs nxt)
	  (recur prs (inc nxt))))]
    (->> (iterate

jneira

;; jneira's solution to http://4clojure.com/problem/67
(defn primes [n]
  (let
      [next-prime
       (fn [prs]
         (letfn
             [(aux [[f & r :as c] nxt]
                   (cond
                    (empty? c) (conj prs nxt)
                    (zero? (mod nxt f)) (recur prs (inc nxt))

jneira

{-# LANGUAGE OverloadedStrings #-}

{- To Run:
   Load in ghci
   :set -XOverloadedStrings (for convenience)
   Execute repl expr -}

import Control.Applicative
import Data.Attoparsec hiding (Result)
import Data.Attoparsec.Char8 (char8, isDigit_w8, isSpace_w8)

jneira

(defn neighbors-of [cell]
  (set (for [dx [-1 0 1] dy [-1 0 1] :when (not (= [dx dy] [0 0]))]
    [(+ dx (first cell)) (+ dy (second cell))])))

(defn alive? [[cell freqs] world]
  (or (and (= 2 freqs) (contains? world cell)) (= 3 freqs)))

(defn tick [world]
  (let [frequencies (frequencies (reduce #(concat %1 (neighbors-of %2)) [] world))]
    (set (keys (filter #(alive? % world) frequencies)))))

jneira

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

(fn winner [board]
  (let [trasp (apply map vector board)
        diag #(map-indexed (fn [x y] (y x)) %)
        all (concat board trasp
                    (map diag [board (reverse board)]))]
    (some #(or (:x %) (:o %)) 
          (filter #(= 1 (count %)) (map set all)))))

jneira

;; jneira's solution to http://4clojure.com/problem/74

(fn squares [s] 
  (let [nums (map read-string (.split s ","))
        sqrs (filter #(= % (Math/pow (Math/sqrt %) 2)) nums)]
    (apply str (interpose "," sqrs))))

jneira

;; jneira's solution to http://4clojure.com/problem/81

(fn [f & r] (set (filter f (apply concat r))))

jneira

;; jneira's solution to Power Set
;; https://4clojure.com/problem/85
;; translated directly from algorithm described in wikipedia :-P

(fn P [S]
  (if (empty? S) #{S}
    (let [e (first S)
          T (disj S e)
          PT (P T)
          F (fn [e T] (set (map #(conj % e)  T)))]

jneira

;; jneira's solution to Transitive Closure
;; https://4clojure.com/problem/84

(fn [s]
  (let [f #(for [[a b] % [c d] %
                 :when (= c b)] [a d])]
    (->> s (iterate #(let [n (into % (f %))]
                       (when (not= % n) n)))
         (take-while identity)
         (last))))