Data commit

Task/Truncatable-primes/Clojure/truncatable-primes.clj

@@ -0,0 +1,41 @@
+(use '[clojure.contrib.lazy-seqs :only [primes]])
+
+(def prime?
+  (let [mem (ref #{})
+	primes (ref primes)]
+    (fn [n]
+      (dosync
+       (if (< n (first @primes))
+	 (@mem n)
+	 (let [[mems ss] (split-with #(<= % n) @primes)]
+	   (ref-set primes ss)
+	   ((commute mem into mems) n)))))))
+
+(defn drop-lefts [n]
+  (let [dropl #(if (< % 10) 0 (Integer. (subs (str %) 1)))]
+    (->> (iterate dropl n)
+	 (take-while pos? ,)
+	 next)))
+
+(defn drop-rights [n]
+  (->> (iterate #(quot % 10) n)
+       next
+       (take-while pos? ,)))
+
+(defn truncatable-left? [n]
+  (every? prime? (drop-lefts n)))
+
+(defn truncatable-right? [n]
+  (every? prime? (drop-rights n)))
+
+user> (->> (for [p primes
+	   :while (< p 1000000)
+	   :when (not-any? #{\0} (str p))
+	   :let [l? (if (truncatable-left? p) p 0)
+		 r? (if (truncatable-right? p) p 0)]
+	    :when (or l? r?)]
+       [l? r?])
+     ((juxt #(apply max-key first %) #(apply max-key second %)) ,)
+     ((juxt ffirst (comp second second)) ,)
+     (map vector ["left truncatable: " "right truncatable: "] ,))
+(["left truncatable: " 998443] ["right truncatable: " 739399])