Mercurial > repos > other > adventofcode2023
annotate day13.rb @ 39:0e17e4bd97a9 default tip
Rewrite as four-dimensional route finding
The grid isn't just a 2D grid. The constraints make it 4D:
* X
* Y
* Last direction
* Number of steps in that direction
By tracking all four dimensions, we can find the shortest route
for _all_ combinations of the constraint. Previously, we were dropping
routes that were currently longer but ended up shorter because
they could take subsequent steps that other routes couldn't.
author | IBBoard <dev@ibboard.co.uk> |
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date | Sun, 22 Sep 2024 11:30:53 +0100 |
parents | fac484765bc9 |
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20
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1 #! /usr/bin/env ruby |
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2 |
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3 if ARGV.length != 1 |
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4 abort("Incorrect arguments - needs input file") |
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5 elsif not File.exist? (ARGV[0]) |
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6 abort("File #{ARGV[0]} did not exist") |
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7 end |
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8 |
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9 file = ARGV[0] |
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10 |
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11 maps = File.open(file, "r").each_line().map(&:chomp).chunk_while {|before, after| before.length == after.length}.filter {|chunk| chunk != [""]}.map {|chunk| chunk.map{|row| row.each_char.to_a}} |
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12 |
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13 def find_reflection(data) |
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14 candidate_start = data.each_cons(2).with_index.flat_map {|vals,idx| a,b = vals; a == b ? [idx] : []} |
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15 valid_starts = candidate_start.flat_map do |start| |
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16 pos = start |
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17 reflected = start + 1 |
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18 match = true |
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19 while pos > 0 and reflected < data.length - 1 |
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20 pos -= 1 |
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21 reflected += 1 |
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22 match = data[pos] == data[reflected] |
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23 break unless match |
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24 end |
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25 match ? [start + 1] : [] |
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26 end |
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27 valid_starts[0] |
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28 end |
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29 |
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30 puts maps.flat_map {|data| [find_reflection(data).to_i * 100, find_reflection(data.transpose()).to_i]}.sum |