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#lang racket
(require advent-of-code
threading)
(define input
(~>(fetch-aoc-input (find-session) 2023 13 #:cache #true)
(string-split "\n\n")
(map (λ~> string-split) _)))
(define (do-symmetric? lefts rights errs)
(cond
[(empty? rights) #f]
[else
(define found-errs
(for/sum ([l (in-string (string-join lefts ""))]
[r (in-string (string-join rights ""))]
#:unless (char=? l r))
1))
(if (= errs found-errs)
(length lefts)
(do-symmetric? (cons (first rights) lefts)
(rest rights)
errs))]))
(define (symmetric? xss errs)
(do-symmetric? (list (first xss)) (rest xss) errs))
(define (transpose strs)
(~> strs
(map string->list _)
(apply map list _)
(map list->string _)))
(define (find-symmetry-score xss errs)
(cond
[(symmetric? xss errs) => (curry * 100)]
[else (symmetric? (transpose xss) errs)]))
;; part 1
(for/sum ([note (in-list input)])
(find-symmetry-score note 0))
;; part 2
(for/sum ([note (in-list input)])
(find-symmetry-score note 1))
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