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(define-module (day25)
#:use-module (ice-9 rdelim)
#:use-module (rnrs io ports)
#:use-module (srfi srfi-1)
#:use-module (srfi srfi-43))
(define +block-chars+ (char-set #\# #\.))
(define (read-key-or-lock port topc expect-end)
(define vec (make-vector 5 0))
(let iter ((i 0))
(unless (= i 5)
(let ((line (read-line port)))
(when (eof-object? line)
(error "Unexpected EOF in the middle of a key."))
(unless (string-every +block-chars+ line)
(error "Lines in keys/locks must be '#' or '.'." line))
(let jiter ((j 0))
(unless (= j 5)
(when (char=? topc (string-ref line j))
(unless (= i (vector-ref vec j))
(error
(string-append "Columns must be all '#' followed by all '.' "
"or vice versa; cannot alternate.")
vec line i j))
(vector-set! vec j (+ i 1)))
(jiter (+ j 1)))))
(iter (+ i 1))))
(define end-line (read-line port))
(unless (equal? end-line expect-end)
(error "Expected key/lock end line to be ~a; got ~a." expect-end end-line))
(define blank (read-line port))
(unless (or (eof-object? blank) (string=? "" blank))
(error "Expected blank line or end-of-file." blank))
vec)
(define (read-key port)
(define line (read-line port))
(cond ((or (eof-object? line) (string=? "" line))
(values (eof-object) (eof-object)))
((string=? line ".....")
(values 'key (read-key-or-lock port #\. "#####")))
((string=? line "#####")
(values 'lock (read-key-or-lock port #\# ".....")))
(else (error "Expected key ('.....') or lock ('#####')." line))))
(define (read-input port)
(let iter ((keys '()) (locks '()))
(define-values (type vec) (read-key port))
(cond ((eof-object? type) (values keys locks))
((eq? type 'key) (iter (cons vec keys) locks))
(else (iter keys (cons vec locks))))))
(define (part1 port)
(define-values (keys locks) (read-input port))
(fold (lambda (key cnt)
(fold (lambda (lock cnt)
(if (vector-every >= key lock) (+ cnt 1) cnt)) cnt locks))
0 keys))
(define (part2 port)
"yay!")
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