56 lines
1.9 KiB
Scheme
56 lines
1.9 KiB
Scheme
(import (rnrs)
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(only (chezscheme) make-parameter parameterize printf))
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(define filename (make-parameter "in/day1"))
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(define (string-reverse str) (list->string (reverse (string->list str))))
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(define default-numbers
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'(("one" . 1) ("two" . 2) ("three" . 3) ("four" . 4) ("five" . 5)
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("six" . 6) ("seven" . 7) ("eight" . 8) ("nine" . 9)))
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(define numbers (make-parameter default-numbers))
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(define (digit? c) (and (char<=? #\0 c #\9) c))
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(define (digit-val c) (- (char->integer c) (char->integer #\0)))
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(define (at? start short&val long)
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(let* [(short (car short&val))
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(val (cdr short&val))
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(end (+ start (string-length short)))]
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(cond [(> end (string-length long)) #f]
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[(string=? short (substring long start end)) val]
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[else #f])))
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(define (find-first str)
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(let loop [(i 0)]
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(cond [(digit? (string-ref str i)) => digit-val]
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[(exists (lambda (n) (at? i n str)) (numbers))]
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[else (loop (+ i 1))])))
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(define (find-last str)
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(let* [(rev-car (lambda (p) (cons (string-reverse (car p)) (cdr p))))
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(rnums (map rev-car (numbers)))
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(rstr (string-reverse str))]
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(parameterize [(numbers rnums)] (find-first rstr))))
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(define (make-value first last) (+ (* 10 first) last))
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(define (value line) (make-value (find-first line) (find-last line)))
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(define (value1 line) (parameterize [(numbers '())] (value line)))
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(define (value2 line) (parameterize [(numbers default-numbers)] (value line)))
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(define (all-lines file)
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(let [(next (lambda () (get-line file)))]
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(do [(line (next) (next))
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(acc '() (cons line acc))]
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[(eof-object? line) (reverse acc)])))
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(define (input) (call-with-input-file (filename) all-lines))
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(define (part1 input) (apply + (map value1 input)))
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(define (part2 input) (apply + (map value2 input)))
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(let [(in (input))] (printf "~a~n~a~n" (part1 in) (part2 in)))
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