110 lines
2.7 KiB
Ruby
110 lines
2.7 KiB
Ruby
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#!/usr/bin/env ruby
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require "debug"
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require "matrix"
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@input = (ARGV.first.nil? ? DATA : ARGF)
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.readlines(chomp: true)
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.map(&:chars)
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start = [@input.flatten.index { _1 == "S" }]
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.map { Vector[_1 / @input.size, _1 % @input.first.size] }
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.first
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finish = [@input.flatten.index { _1 == "E" }]
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.map { Vector[_1 / @input.size, _1 % @input.first.size] }
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.first
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NORTH = Vector[-1, 0]
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EAST = Vector[0, +1]
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SOUTH = Vector[+1, 0]
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WEST = Vector[0, -1]
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DIRECTIONS = [NORTH, EAST, SOUTH, WEST]
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class PriorityQueue < Array
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alias extract_min shift
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alias peek first
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def <<(v)
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unless v.is_a?(Array)
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raise ArgumentError, "PriorityQueue requires array with priority as last"
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end
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super
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sort_by!(&:last)
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end
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end
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def dijkstra(graph, start, start_direction, target)
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dist = Hash.new # scores
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prev = Hash.new
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queue = PriorityQueue.new
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queue << [start, start_direction, 0]
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dist[[start, start_direction]] = 0
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# alternate only inserting source and add nodes inside score check later
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until queue.empty?
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position, direction, score = queue.extract_min
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neighbors = DIRECTIONS.each do |new_direction|
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neighbor = position + new_direction
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next if neighbor == position || graph.dig(*neighbor) == "#"
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new_score = score + 1 + (direction == new_direction ? 0 : 1) * 1_000
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if dist[[neighbor, new_direction]].nil? || new_score < dist[[neighbor, new_direction]]
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dist[[neighbor, new_direction]] = new_score
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prev[[neighbor, new_direction]] = [[position, direction]]
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queue << [neighbor, new_direction, new_score]
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elsif new_score == dist[[neighbor, new_direction]]
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prev[[neighbor, new_direction]] << [position, direction]
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end
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end
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end
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return dist, prev
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end
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def seats(dist, prev, target)
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visited, queue = Array.new, Array.new
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lowest_score = dist.keys.select { |(pos, dir)| pos == target }.map { dist[_1] }.min
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dist
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.select { |(position, _), score| position == target && lowest_score == score }
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.each { queue << _1.first }
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until queue.empty?
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directional_location = queue.pop
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visited << directional_location.first
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unless prev[directional_location].nil?
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queue.concat(prev[directional_location])
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end
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end
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return visited.uniq
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end
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dist, prev = dijkstra(@input, start, EAST, finish)
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part_1 = dist.keys.select { |(pos, dir)| pos == finish }.map { dist[_1] }.min
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p part_1
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part_2 = seats(dist, prev, finish)
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p part_2.size
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__END__
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###############
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#.......#....E#
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#.#.###.#.###.#
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#.....#.#...#.#
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#.###.#####.#.#
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#.#.#.......#.#
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#.#.#####.###.#
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#...........#.#
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###.#.#####.#.#
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#...#.....#.#.#
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#.#.#.###.#.#.#
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#.....#...#.#.#
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#.###.#.#.#.#.#
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#S..#.....#...#
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###############
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