blob: 53ca9eefc82d5361d2bb659ed5544043af3e1be1 (
plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
|
#lang racket
(require advent-of-code
threading)
(match-define (list times distances)
(~> (open-aoc-input (find-session) 2023 6 #:cache #true) port->lines))
;; part 1
(define get-numbers (λ~> string-split (map string->number _) rest))
(define (find-bound race-time dist button-time step)
(if (< dist (* button-time (- race-time button-time)))
button-time
(find-bound race-time dist (+ step button-time) step)))
(define (lower-bound rtime dist)
(find-bound rtime dist 1 1))
(define (upper-bound rtime dist)
(find-bound rtime dist rtime -1))
(for/fold ([acc 1])
([race-time (in-list (get-numbers times))]
[distance (in-list (get-numbers distances))])
(* acc (add1 (- (upper-bound race-time distance) (lower-bound race-time distance)))))
;; part 2
(define unkern (λ~>> get-numbers (apply ~a) string->number))
(define big-time (unkern times))
(define big-distance (unkern distances))
(add1 (- (upper-bound big-time big-distance) (lower-bound big-time big-distance)))
|
