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Dimitri Lozeve 2024-11-12 21:43:32 +01:00
commit f242d2b0df
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2021/day10/day10.scm Normal file
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(import (chicken io)
(chicken sort)
srfi-1
matchable)
(define (read-input #!optional (port (current-input-port)))
(read-lines port))
(define (check str)
(let lp ((stack '())
(input (string->list str)))
(match (list stack input)
((() ()) #t)
(((#\( . srest) (#\) . irest)) (lp srest irest))
(((#\[ . srest) (#\] . irest)) (lp srest irest))
(((#\{ . srest) (#\} . irest)) (lp srest irest))
(((#\< . srest) (#\> . irest)) (lp srest irest))
((_ (#\( . irest)) (lp (cons #\( stack) irest))
((_ (#\[ . irest)) (lp (cons #\[ stack) irest))
((_ (#\{ . irest)) (lp (cons #\{ stack) irest))
((_ (#\< . irest)) (lp (cons #\< stack) irest))
((_ ()) stack)
((_ _) (car input)))))
(define (check-score c)
(match c
(#\) 3)
(#\] 57)
(#\} 1197)
(#\> 25137)
(_ 0)))
(define (part1 in)
(apply + (map check-score (map check in))))
(define (completion-value c)
(match c
(#\( 1)
(#\[ 2)
(#\{ 3)
(#\< 4)
(_ 0)))
(define (completion-score lst)
(foldl (lambda (acc c) (+ (* 5 acc) (completion-value c))) 0 lst))
(define (part2 in)
(let ((scores (map completion-score (filter list? (map check in)))))
(list-ref (sort scores <) (/ (sub1 (length scores)) 2))))
(let ((in (read-input)))
(print (part1 in))
(print (part2 in)))