aoc2020/10.rkt

#lang curly-fn racket

(require "scripts/aoc.rkt")

;; solution for day 10

;; helper functions here

(define (part1 input)
  (define sorted (sort input <))
  (define-values [_ ones threes]
    (for/fold ([prev 0] [ones 0] [threes 0]) ([x (in-list sorted)])
      (values x (+ ones (if (= 1 (- x prev)) 1 0))
              (+ threes (if (= 3 (- x prev)) 1 0)))))
  ; (displayln ones)
  ; (displayln (add1 threes))
  (* ones (add1 threes)))

; (part1 '(16
;          10
;          15
;          5
;          1
;          11
;          7
;          19
;          6
;          12
;          4))
; (part1 '(28
;          33
;          18
;          42
;          31
;          14
;          46
;          20
;          48
;          47
;          24
;          23
;          49
;          45
;          19
;          38
;          39
;          11
;          1
;          32
;          25
;          35
;          8
;          17
;          7
;          9
;          4
;          2
;          34
;          10
;          3))

  ; (struct res [val ones threes] #:transparent)
  ; (define (step input [prev 0])
  ;   ; (printf "~a ~a ~a\n" (first input) (second input) (third input))
  ;   (define res3
  ;     (if (and (> (length input) 2) (<= (- (third input) 3) prev))
  ;       (step (cons (first input) (rest (rest (rest input)))) (third input))
  ;       #f))
  ;   (define res2
  ;     (if (and (> (length input) 1) (<= (- (second input) 3) prev))
  ;       (step (rest (rest input)) (second input))
  ;       #f))
  ;   (define res1
  ;     (if (and (> (length input) 0) (<= (- (first input) 3) prev))
  ;       (step (rest input) (first input))
  ;       #f))
  ;   (define n1 (and res1 (res-val res1)))
  ;   (define n2 (and res2 (res-val res2)))
  ;   (define n3 (and res3 (res-val res3)))
  ;   (cond
  ;     [(and res1 (and res2 (>= n1 n2)) (and res3 (>= n1 n3))) (res (add1 n1) (add1 (res-ones res1)) (res-threes res1))]
  ;     [(and res2 (and res1 (>= n2 n1)) (and res3 (>= n2 n3))) (res (add1 n1) (res-ones res1) (res-threes res1))]
  ;     [(and res3 (and res1 (>= n3 n1)) (and res2 (>= n3 n2))) (res (add1 n1) (res-ones res1) (add1 (res-threes res1)))]
  ;     [else (res 1 0 0)]))
  ; (define res_ (step sorted))
  ; (* (res-ones res_) (res-threes res_)))

(define (part2 input)
  (define is (cons 0 (sort input <)))
  (define-values [edges _]
    (for/fold ([edges '()] [lst (rest is)]) ([x (in-list is)])
      (define res3
        (if (and (> (length lst) 2) (<= (- (third lst) 3) x))
          (list (list x (third lst)))
          '()))
      (define res2
        (if (and (> (length lst) 1) (<= (- (second lst) 3) x))
          (list (list x (second lst)))
          '()))
      (define res1
        (if (and (> (length lst) 0) (<= (- (first lst) 3) x))
          (list (list x (first lst)))
          '()))
    (values (append edges res1 res2 res3) (if (empty? lst) '() (rest lst)))))

  (define G (directed-graph edges))

  (define wanted (last is))

  (define memo (make-hash))
  (define (count-paths G node)
    (cond [(hash-has-key? memo node) (hash-ref memo node)]
          [(= node wanted) 1]
          [else
            (define ans (for/sum ([x (in-neighbors G node)])
                          (count-paths G x)))
            (hash-set! memo node ans)
            ans]))

  (count-paths G 0))

; (part2 '(16
;          10
;          15
;          5
;          1
;          11
;          7
;          19
;          6
;          12
;          4))

(module+ test
  (require rackunit)
  ;; tests here
  (displayln "no tests :("))

(module+ main
  (define input (map string->number (file->lines "inputs/10")))
  ;; part 1
  (answer 10 1 (part1 input))

  ;; part 2
  (answer 10 2 (part2 input))

  (displayln "meow"))