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day 14

master
Dustin Swan 12 months ago
parent
commit
eb202d2abc
Signed by: dustinswan GPG Key ID: AB49BD6B2B3A6377
  1. 104
      day14.rkt
  2. 18
      day14.test.txt
  3. 102
      day14.txt

104
day14.rkt

@ -0,0 +1,104 @@
#lang racket
(define input
(let* ([lines (file->lines "day14.txt")]
[template (first lines)]
[rule-strings (drop lines 2)]
[rules (map (λ (rs) (string-split rs " -> ")) rule-strings)])
(list template rules)))
(define template (first input))
(define rules (second input))
(define (find-pairs template)
(reverse
(foldl (λ (el acc) (cons (substring template el (+ 2 el)) acc))
'()
(range 0 (sub1 (string-length template))))))
(define (find-inserts pairs rules)
(map (λ (p) (second (assoc p rules))) pairs))
(define (insert-pairs template inserts)
(foldl (λ (idx acc)
(let* ([x (string (string-ref template idx))]
[insert (list-ref (append inserts (list "")) idx)])
(string-append acc x insert)))
"" (range 0 (string-length template))))
(define (step template rules)
(let* ([pairs (find-pairs template)]
[inserts (find-inserts pairs rules)]
[next (insert-pairs template inserts)])
next))
(define (element-counts str)
(let* ([lst (map string (string->list str))]
[ht (make-hash)])
(for-each (λ (x) (hash-set! ht x (+ 1 (hash-ref ht x 0)))) lst)
ht))
(define part1
(let* ([final (foldl (λ (i acc) (step acc rules)) template (range 0 10))]
[counts (element-counts final)]
[values (hash-values counts)]
[minimum (apply min values)]
[maximum (apply max values)]
[diff (- maximum minimum)])
diff))
part1
; PART 2
; uhoh. start over
(define (inc-hash ht key amount)
(hash-set! ht key (+ amount (hash-ref! ht key 0))))
(define (dec-hash ht key amount)
(hash-set! ht key (- (hash-ref! ht key 0) amount)))
(define (step2 ht)
(define pairs (filter (λ (p) (> (cdr p) 0)) (hash->list ht)))
(for-each (λ (pair-and-count)
(let* ([pair (car pair-and-count)]
[count (cdr pair-and-count)]
[ins (second (assoc pair rules))]
[new1 (string-append (substring pair 0 1) ins)]
[new2 (string-append ins (substring pair 1 2))])
(inc-hash ht new1 count)
(inc-hash ht new2 count)
(dec-hash ht pair count)))
pairs)
ht)
(define (pairs->element-counts ht)
(let* ([el-ht (make-hash)]
[pair-counts (hash->list ht)])
(for-each (λ (p) (let* ([pair (car p)]
[el1 (substring pair 0 1)]
[el2 (substring pair 1 2)]
[count (cdr p)])
(inc-hash el-ht el1 count)
(inc-hash el-ht el2 count)))
pair-counts)
el-ht))
(define part2
(let* ([ht (make-hash)]
[pairs (find-pairs template)]) ; find the initial pairs in the template
(for-each (λ (pair) (inc-hash ht pair 1)) pairs) ; add them to the hash table
(let* ([res (foldl (λ (el acc) (step2 acc)) ht (range 0 40))] ; step!
[el-counts (pairs->element-counts res)]
[first-char (substring template 0 1)]
[last-char (substring template (sub1 (string-length template)))])
(inc-hash el-counts first-char 1) ; add the first..
(inc-hash el-counts last-char 1) ; and last chars twice..
(let* ([lst (hash-map el-counts (λ (key val) (list key (/ val 2))))] ; then divide everything by 2
[values (map second lst)]
[minimum (apply min values)]
[maximum (apply max values)]
[diff (- maximum minimum)])
diff))))
part2

18
day14.test.txt

@ -0,0 +1,18 @@
NNCB
CH -> B
HH -> N
CB -> H
NH -> C
HB -> C
HC -> B
HN -> C
NN -> C
BH -> H
NC -> B
NB -> B
BN -> B
BB -> N
BC -> B
CC -> N
CN -> C

102
day14.txt

@ -0,0 +1,102 @@
BNSOSBBKPCSCPKPOPNNK
HH -> N
CO -> F
BC -> O
HN -> V
SV -> S
FS -> F
CV -> F
KN -> F
OP -> H
VN -> P
PF -> P
HP -> H
FK -> K
BS -> F
FP -> H
FN -> V
VV -> O
PS -> S
SK -> N
FF -> K
PK -> V
OF -> N
VP -> K
KB -> H
OV -> B
CH -> F
SF -> F
NH -> O
NC -> N
SP -> N
NN -> F
OK -> S
BB -> S
NK -> S
FH -> P
FC -> S
OB -> P
VS -> P
BF -> S
HC -> V
CK -> O
NP -> K
KV -> S
OS -> V
CF -> V
FB -> C
HO -> S
BV -> V
KS -> C
HB -> S
SO -> N
PH -> C
PN -> F
OC -> F
KO -> F
VF -> V
CS -> O
VK -> O
FV -> N
OO -> K
NS -> S
KK -> C
FO -> S
PV -> S
CN -> O
VC -> P
SS -> C
PO -> P
BN -> N
PB -> N
PC -> H
SH -> K
BH -> F
HK -> O
VB -> P
NV -> O
NB -> C
CP -> H
NO -> K
PP -> N
CC -> S
CB -> K
VH -> H
SC -> C
KC -> N
SB -> B
BP -> P
KP -> K
SN -> H
KF -> K
KH -> B
HV -> V
HS -> K
NF -> B
ON -> H
BO -> P
VO -> K
OH -> C
HF -> O
BK -> H
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