aoc2023-day6.scm

(use-modules (srfi srfi-1) (ice-9 textual-ports) (ice-9 format) (ice-9 pretty-print))

(define (read-input)
  (let ([line (get-line (current-input-port))])
    (if (eof-object? line)
	'()
	(cons (map string->number (string-tokenize line char-set:digit))
	      (read-input)))))

(define (count-wins race-pair)
  (fold + 0 (map (λ (time)
		   (if (>= (* time (- (car race-pair) time))
			   (cadr race-pair))
		       1 0))
		 (iota (1- (car race-pair)) 1))))

(define (part1 input)
  (fold * 1 (map count-wins (zip (car input)
				 (cadr input)))))

(define (%combine-numbers lst)
  (string->number (string-concatenate (map number->string lst))))

(define (part2 input)
  (count-wins (list (%combine-numbers (car input))
		    (%combine-numbers (cadr input)))))

(let* ([input (read-input)])
  (format #t "Part 1: ~a~%" (part1 input))
  (format #t "Part 2: ~a~%" (part2 input)))