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annotate day9.rb @ 39:0e17e4bd97a9 default tip

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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>
date Sun, 22 Sep 2024 11:30:53 +0100
parents 891878e52a31
children
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891878e52a31 Implement Day 9 - diffing and predicting
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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 histories = File.open(file, "r").each_line(chomp: true).map {|line| line.split(" ").map(&:to_i)}
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13 def diff_array(arr)
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14 arr.each_cons(2)
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16 end
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17
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18 predictions = histories.map do |history|
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19 vals = history
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20 layers = [history]
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21 while not vals.all? {|v| v == 0}
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22 vals = vals.each_cons(2).map {|a,b| b - a}
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23 layers << vals
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24 end
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25 layers.reverse!.each_cons(2).map {|diffs, vals| vals << diffs[-1] + vals[-1]}
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26 layers[-1][-1]
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27 end
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29 puts predictions.sum
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30 # Rest of algorithm here