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#!/usr/bin/env -S guile -s
!#
(use-modules (ice-9 regex)
(ice-9 textual-ports)
(srfi srfi-1))
(define (read-lines port)
(letrec ((loop (lambda (l ls)
(if (eof-object? l)
ls
(loop (get-line port) (cons l ls))))))
(reverse (loop (get-line port) '()))))
(define (matches-for-line line regex)
(letrec ((loop (lambda (l ls)
(if (not l) ls
(loop (string-match regex line (match:end l)) (cons l ls))))))
(loop (string-match regex line) '())))
(define (find-candidates lines)
(let ((i -1))
(concatenate (map-in-order (lambda (line) (let ((cands (matches-for-line line "[0-9]+")))
(set! i (+ i 1))
(map (lambda (cand)
`(,i ,(match:start cand) ,(- (match:end cand) (match:start cand)) ,(string->number (match:substring cand)))) cands))) lines))))
(define (find-gears lines)
(let ((i -1))
(concatenate (map-in-order (lambda (line) (let ((cands (matches-for-line line "\\*")))
(set! i (+ i 1))
(map (lambda (cand)
`(,i ,(match:start cand))) cands))) lines))))
(define (parts-for-gear parts gear)
(filter (lambda (part)
(and (>= (car part) (- (car gear) 1))
(<= (car part) (+ (car gear) 1))
(<= (- (cadr gear) (cadr part)) (caddr part))
(>= (- (cadr gear) (cadr part)) -1))) parts))
(let* ((port (open-input-file "3.txt"))
(lines (read-lines port))
(parts (find-candidates lines)))
(close-port port)
(display (fold + 0 (map (lambda (x) (* (car x) (cadr x))) (filter (lambda (x) (= (length x) 2)) (map (lambda (gear) (map cadddr (parts-for-gear parts gear))) (find-gears lines)))))))
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