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annotate day6b.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 6e0615e54e71
children
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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 time, distance = File.open(file, "r").each_line(chomp: true).map {|v| v.split(":")[1].split(" ").join("").to_i}
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12 events = [[time, distance]]
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13
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14 product = events.map do |event|
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15 mid = (event[0].to_f / 2).floor
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16 first_success = (1..mid).bsearch {|i| (event[0] - i) * i > event[1]}
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17 num_success = (mid - first_success + 1) * 2
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18 event[0].odd? ? num_success : num_success - 1
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19 end.reduce(:*)
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20
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21 puts product