Mercurial > repos > other > adventofcode2023
view day9b.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> |
---|---|
date | Sun, 22 Sep 2024 11:30:53 +0100 |
parents | 891878e52a31 |
children |
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#! /usr/bin/env ruby if ARGV.length != 1 abort("Incorrect arguments - needs input file") elsif not File.exist? (ARGV[0]) abort("File #{ARGV[0]} did not exist") end file = ARGV[0] histories = File.open(file, "r").each_line(chomp: true).map {|line| line.split(" ").map(&:to_i)} def diff_array(arr) arr.each_cons(2) end predictions = histories.map do |history| vals = history layers = [history] while not vals.all? {|v| v == 0} vals = vals.each_cons(2).map {|a,b| b - a} layers << vals end layers.reverse!.each_cons(2).map {|diffs, vals| vals.insert(0, vals[0] - diffs[0])} layers[-1][0] end puts predictions.sum # Rest of algorithm here