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  1. (def my-solution2
  2.  
  3.   (fn [start]
  4.     (let [str-start (str start)
  5.           start-a? (-> str-start count odd?)
  6.           ;_ (println :start-a? start-a?)
  7.           start-stage-pow (dec (Math/ceil (/ (count str-start) 2)))
  8.           ;_ (println :start-stage-pow start-stage-pow)
  9.           start-stage (Math/pow 10 start-stage-pow)
  10.           ;_ (println :start-stage start-stage)
  11.           str-start-left (clojure.string/join (take (inc start-stage-pow) str-start))
  12.           ;_ (println :str-start-left str-start-left)
  13.           start-stage-end (* 10 start-stage)
  14.           ;_ (println :start-stage-end start-stage-end)
  15.           start-left (inc (Long/parseLong str-start-left))
  16.           ;_ (println :start-left start-left)
  17.           start-palindrome (if start-a?
  18.                            (clojure.string/join (cons str-start-left (reverse (butlast str-start-left))))
  19.                            (clojure.string/join (cons str-start-left (reverse str-start-left))))
  20.           ;_ (println :start-palindrome start-palindrome)
  21.           ]
  22.  
  23.       (filter #(>= % start)
  24.               (map #(Long/parseLong (first %))
  25.                    (iterate
  26.                      (fn [[palindrome, a? stage stage-end left]]
  27.  
  28.                        (let [stage-end? (= (inc left) stage-end)
  29.  
  30.                              new-a? (if stage-end? (not a?) a?)
  31.                              new-stage (if (and
  32.                                              (not a?)
  33.                                              stage-end?) (* 10 stage) stage)
  34.                              new-left (if stage-end? new-stage (inc left))
  35.  
  36.                              str-left (str left)
  37.                              new-palindrome (if a?
  38.                                               (clojure.string/join (cons str-left (reverse (butlast str-left))))
  39.                                               (clojure.string/join (cons str-left (reverse str-left))))
  40.  
  41.                              ret-val [new-palindrome
  42.                                       new-a?
  43.                                       new-stage
  44.                                       (* 10 new-stage)
  45.                                       new-left]
  46.                              ]
  47.                          ret-val
  48.  
  49.                          ))
  50.                      ; initial values
  51.                      [start-palindrome
  52.                       start-a?
  53.                       (int start-stage) (int start-stage-end),
  54.                       start-left]
  55.                      )))))
  56.  
  57. )
  58.  
  59. (time (println (take 1 (my-solution2 (* 111111111 111111111)))))
Success #stdin #stdout 1.58s 389120KB
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Standard input is empty
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(12345678987654321)
"Elapsed time: 22.487728 msecs"
https://ideone.com/ZJeBik
language:
Clojure (clojure 1.10.0)
created:
12 years ago
visibility:
public

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