feat(tazjin/aoc2020): Add (somewhat delayed...) solution for day 7

Solve time is like 36 hours, that must be a record!

Change-Id: I3713f033d83e6179a5d5fa7513952ee3864a6164
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2238
Reviewed-by: tazjin <mail@tazj.in>
Tested-by: BuildkiteCI
This commit is contained in:
Vincent Ambo 2020-12-08 23:25:05 +01:00 committed by tazjin
parent 42405bfa24
commit 3061b3228f

View file

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;; Advent of Code 2020 - Day 7
(require 'cl-lib)
(require 'dash)
(require 'f)
(require 's)
(require 'ht)
(defvar day7/input
(s-lines (s-chomp (f-read "/tmp/aoc/day7.txt"))))
(defun day7/parse-bag (input)
(string-match (rx line-start
(group (one-or-more (or letter space)))
"s contain "
(group (one-or-more anything))
"." line-end)
input)
(cons (match-string 1 input)
(-map
(lambda (content)
(unless (equal content "no other bags")
(progn
(string-match
(rx (group (one-or-more digit))
space
(group (one-or-more anything) "bag"))
content)
(cons (match-string 2 content)
(string-to-number (match-string 1 content))))))
(s-split ", " (match-string 2 input)))))
(defun day7/id-or-next (table bag-type)
(unless (ht-contains? table bag-type)
(ht-set table bag-type (length (ht-keys table))))
(ht-get table bag-type))
(defun day7/build-graph (input &optional flip)
"Represent graph mappings directionally using an adjacency
matrix, because that's probably easiest.
By default an edge means 'contains', with optional argument
FLIP edges are inverted and mean 'contained by'."
(let ((bag-mapping (ht-create))
(graph (let ((length (length input)))
(apply #'vector
(-map (lambda (_) (make-vector length 0)) input)))))
(cl-loop for bag in (-map #'day7/parse-bag input)
for bag-id = (day7/id-or-next bag-mapping (car bag))
do (-each (-filter #'identity (cdr bag))
(pcase-lambda (`(,contained-type . ,count))
(let ((contained-id (day7/id-or-next bag-mapping contained-type)))
(if flip
(aset (aref graph contained-id) bag-id count)
(aset (aref graph bag-id) contained-id count))))))
(cons bag-mapping graph)))
;; Puzzle 1
(defun day7/find-ancestors (visited graph start)
(ht-set visited start t)
(cl-loop for bag-count being the elements of (aref graph start)
using (index bag-id)
when (and (> bag-count 0)
(not (ht-contains? visited bag-id)))
do (day7/find-ancestors visited graph bag-id)))
(message
"Solution to day7/1: %s"
(pcase-let* ((`(,mapping . ,graph) (day7/build-graph day7/input t))
(shiny-gold-id (ht-get mapping "shiny gold bag"))
(visited (ht-create)))
(day7/find-ancestors visited graph shiny-gold-id)
(- (length (ht-keys visited)) 1)))
;; Puzzle 2
(defun ht-find-by-value (table value)
(ht-find (lambda (_key item-value) (equal item-value value)) table))
(defun day7/count-contained-bags (mapping graph start)
(cl-loop for bag-count being the elements of (aref graph start)
using (index bag-id)
when (> bag-count 0)
sum (+ bag-count
(* bag-count (day7/count-contained-bags mapping graph bag-id)))))
(message "Solution to day7/2: %s"
(pcase-let* ((`(,mapping . ,graph) (day7/build-graph day7/input))
(shiny-gold-id (ht-get mapping "shiny gold bag")))
(day7/count-contained-bags mapping graph shiny-gold-id)))