Mercurial > repos > other > adventofcode2023
view 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> |
---|---|
date | Sun, 22 Sep 2024 11:30:53 +0100 |
parents | fac484765bc9 |
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] 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}} def find_reflection(data) candidate_start = data.each_cons(2).with_index.flat_map {|vals,idx| a,b = vals; a == b ? [idx] : []} valid_starts = candidate_start.flat_map do |start| pos = start reflected = start + 1 match = true while pos > 0 and reflected < data.length - 1 pos -= 1 reflected += 1 match = data[pos] == data[reflected] break unless match end match ? [start + 1] : [] end valid_starts[0] end puts maps.flat_map {|data| [find_reflection(data).to_i * 100, find_reflection(data.transpose()).to_i]}.sum