73 lines
2.4 KiB
Racket
73 lines
2.4 KiB
Racket
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#lang racket
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; You try to ask why they can't just use a weather machine ("not powerful enough")
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; and where they're even sending you ("the sky") and why your map looks mostly
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; blank ("you sure ask a lot of questions") and hang on did you just say the sky
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; ("of course, where do you think snow comes from") when you realize that the
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; Elves are already loading you into a trebuchet ("please hold still, we need
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; to strap you in").
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; As they're making the final adjustments, they discover that their calibration
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; document (your puzzle input) has been amended by a very young Elf who was
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; apparently just excited to show off her art skills. Consequently, the Elves
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; are having trouble reading the values on the document.
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; The newly-improved calibration document consists of lines of text; each line
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; originally contained a specific calibration value that the Elves now need to
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; recover. On each line, the calibration value can be found by combining the
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; first digit and the last digit (in that order) to form a single two-digit
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; number.
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; For example:
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; 1abc2
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; pqr3stu8vwx
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; a1b2c3d4e5f
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; treb7uchet
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; In this example, the calibration values of these four lines are 12, 38, 15,
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; and 77. Adding these together produces 142.
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; Consider your entire calibration document. What is the sum of all of the
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; calibration values?
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(define input '("1abc2"
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"pqr3stu8vwx"
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"a1b2c3d4e5f"
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"treb7uchet"))
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; From a char list returns the first digit it finds as a char, or nil
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(define (get-first-digit list)
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(if (= (length list) 0)
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null
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(let ([current-char (first list)])
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(if (char-numeric? current-char)
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current-char
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(get-first-digit (rest list))))))
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(define (get-last-digit list carry)
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(if (= (length list) 0)
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carry
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(let* ([current-char (first list)]
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[next-char
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(if (char-numeric? current-char)
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current-char
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carry)])
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(get-last-digit (rest list) next-char))))
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; Creates a new number from the first & last number found inside a string
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(define (list->digits list)
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(let ([first-char (get-first-digit list)]
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[last-char (get-last-digit list -1)])
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(string->number (string first-char last-char))))
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(define char-list (map string->list input))
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(define result (foldl + 0 (map list->digits char-list)))
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(print result)
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