Advent of Code, Day 2, Part II

advent-02.rkt

#lang racket
(define in "...")

(count (λ (x)
         (match (regexp-match #rx"([0-9]*)-([0-9]*) ([a-z]): (.*)" x)
           [(list _
                  (app string->number low)
                  (app string->number high)
                  (app string->list (list a))
                  (app string->list cs))
            (xor (char=? a (list-ref cs (sub1 low)))
                 (char=? a (list-ref cs (sub1 high))))]))
       (with-input-from-string in port->lines))