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