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00 Digit search.md

Digit search

This is one of those weird programming puzzles with no real point except practice. But it's considered Very Hard in JavaScript. Let's see how we do in Clojure.

Write a function that takes a sequence of integers. You're trying to get all 10 digits by looking through the numbers sequentially. When you have found one instance of every decimal digit, return whatever number you were on when you found the last one. If you get to the end of the sequence without finding all the digits (for instance, maybe there was no 9), then just return nil.

Example

(digit-search   [5175 4538 2926 5057 6401 4376 2280 6137]) ;=> 5057
;; digits found: 517- 4-38 29-6 -0

(digit-search   [5719 7218 3989 8161 2676 3847 6896 3370]) ;=> 3370
;; digits found: 5719 -2-8 3--- --6- ---- --4- ---- ---0

(digit-search   [4883 3876 7769 9846 9546 9634 9696 2832]) ;=> nil
;; digits found: 48-3 --76 ---9 ---- -5-- ---- ---- 2---
;; 0 and 1 are missing

Thanks to this site for the challenge idea where it is considered Very Hard level in JavaScript.

Ugly but it works hihi

(defn digits
  [number]
  (if (< number 10)
    [number]
    (conj (digits (quot number 10)) (rem number 10))))


(defn digit-search
  ([numbers] (digit-search numbers #{}))
  ([numbers decimals]
   (let [number (first numbers)]
     (if (not number)
       nil
       (let [digits (digits number)
             updated-decimals (reduce conj decimals digits)]
         (if (= 10 (count updated-decimals))
           number
           (digit-search (rest numbers) updated-decimals)))))))