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00 First before second.md

First before second

Write a function that takes a string and two letters. The function should return true if every instance of the first letter comes before every instance of the second letter.

Examples

(first-before? "A rabbit jumps joyfully" \a \j) ;=> true
(first-before? "A jolly rabbit jumps joyfully" \a \j) ;=> false
(first-before? "Don't tread on me" \t \m) ;=> true
(first-before? "Every React podcast" \t \d) ;=> false

Notes

• Letters will be mixed case. You should treat \A the same as \a.
• You can assume the strings will contain instances of both letters.

Thanks to this site for the challenge idea where it is considered Hard in Python.

Please submit your solutions as comments on this gist.

(defn first-before? [s c1 c2]
  (let [regex           (re-pattern (str c1 \| c2))
        matches         (re-seq regex (str/lower-case s))
        [group1 group2] (partition-by identity matches)]
    (and (= (str c1) (first group1))
         (= (str c2) (first group2)))))

@diavoletto76 Your solution is my favorite by far! I didn't even consider leaning on those clojure.string functions. Only nitpick is that you seem to have forgotten to make it case insensitive :)

@chopmo You are right. Thank you for pointing the case sensitivity issue out.

(defn first-before?
  [s a b]
  (let [ lc clojure.string/lower-case
        a-pos (filter (complement nil?) (map-indexed #(if (= (lc a) (lc %2)) %1 nil) s))
        b-pos (filter (complement nil?) (map-indexed #(if (= (lc b) (lc %2)) %1 nil) s))
        all (concat a-pos b-pos)]
    (= all (sort all))))

@diavoletto76 your solution is great.