453 PurelyFunctional.tv Newlsetter

00 Backspace jam.md

Backspace jam

Let's say we have users typing keys on the keyboard. We capture the characters they represent in strings. However, sometimes the user hits the backspace key, which removes the previous character. We will represent a backspace key press with a # character. Write a function that applies the behavior of backspace to the string.

Examples

(apply-bs "abc#") ;=> "ab"
(apply-bs "abc###") ;=> ""
(apply-bs "###abc") ;=> "abc"
(apply-bs "there###eir") ;=> "their"

Thanks to this site for the problem idea, where it is rated Hard in Java. The problem has been modified.

Please submit your solutions as comments on this gist.

To subscribe: https://purelyfunctional.tv/newsletter/

Not pretty, but fast:

(defn apply-bs [^String s]
  (loop [sb (StringBuilder. s) octo (.indexOf s "#")]
    (cond (pos? octo) (let [sb (.delete sb (dec octo) (inc octo))]
                        (recur sb (.indexOf sb "#" (dec octo))))
          (neg? octo) (.toString sb)
          :else  (let [sb (.deleteCharAt sb 0)]
                   (recur sb (.indexOf sb "#"))))))