diff options
| -rw-r--r-- | challenge-147/tyler-wardhaugh/clojure/src/c147/t2.clj | 34 | ||||
| -rw-r--r-- | challenge-147/tyler-wardhaugh/clojure/test/c147/t2_test.clj | 7 |
2 files changed, 41 insertions, 0 deletions
diff --git a/challenge-147/tyler-wardhaugh/clojure/src/c147/t2.clj b/challenge-147/tyler-wardhaugh/clojure/src/c147/t2.clj new file mode 100644 index 0000000000..6dc9b4ce63 --- /dev/null +++ b/challenge-147/tyler-wardhaugh/clojure/src/c147/t2.clj @@ -0,0 +1,34 @@ +(ns c147.t2 + (:import [java.util Collections])) + +(def MAX 5000) + +; source: https://oeis.org/A000326 +; definition: +; a(0) = 0, a(1) = 1; for n >= 2, a(n) = 2*a(n-1) - a(n-2) + 3 +; Miklos Kristof, Mar 09 2005 +(defn pentagon-numbers + [] + (let [pents (promise) + f (fn [n-2 n-1] (+ (- (* 2 n-1) n-2) 3))] + @(doto pents + (deliver (list* 0 1 (lazy-seq (map f @pents (rest @pents)))))))) + +(defn in? + [n coll] + (pos? (Collections/binarySearch coll n))) + +(defn suitable-pair? + "Are both n+m and |n-m| pentagonal numbers?" + [n m pents] + (and (in? (+ n m) pents) (in? (abs (- n m)) pents) [n m])) + +(defn find-suitable-pair + [] + (let [pents (into [] (comp (drop 1) (take MAX)) (pentagon-numbers))] + (-> (fn [n] (->> pents (some #(suitable-pair? n % pents)))) + (some pents)))) + +(defn -main + [& _] + (println (find-suitable-pair))) diff --git a/challenge-147/tyler-wardhaugh/clojure/test/c147/t2_test.clj b/challenge-147/tyler-wardhaugh/clojure/test/c147/t2_test.clj new file mode 100644 index 0000000000..0670ed643c --- /dev/null +++ b/challenge-147/tyler-wardhaugh/clojure/test/c147/t2_test.clj @@ -0,0 +1,7 @@ +(ns c147.t2-test + (:require [clojure.test :refer [deftest is testing]] + [c147.t2 :refer [find-suitable-pair]])) + +(deftest target + (testing "Target identified in task description" + (is (= [1560090 7042750] (find-suitable-pair))))) |