aoc2023/6.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt" math/number-theory)

;; solution for day 6

(define *fudge* 1e-10)

(define (do-race time dist)
  (match-define (list lower upper) (quadratic-solutions 1 (- time) dist))
  (~> (- (floor (- upper *fudge*)) (ceiling (+ lower *fudge*)))
      add1 inexact->exact))

(define (part1 input)
  (for/product ([time (in-list (first input))]
                [dist (in-list (second input))])
    (do-race time dist)))

(define (number-concat l)
  (~>> (map number->string l)
       (apply string-append)
       string->number))

(define (part2 input)
  (apply do-race (map number-concat input)))

(define (parse fname)
  (map #{map string->number (rest (string-split %))}
       (file->lines fname)))

; (dbg (part1 (parse "inputs/6-test1")))
; (error)

(module+ main
  (define input (parse "inputs/6"))
  (answer 6 1 (time (part1 input)))
  (answer 6 2 (time (part2 input)))
  (displayln "meow"))