116 lines
1.9 KiB
Ruby
116 lines
1.9 KiB
Ruby
# frozen_string_literal: true
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input = File.read(File.join(__dir__, 'input'))
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class AsteroidBelt
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def initialize(text)
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@grid = parse(text)
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end
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def asteroids
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return @asteroids unless @asteroids.nil?
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@asteroids = []
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@grid.each_with_index do |line, y|
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line.chars.each_with_index do |cell, x|
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@asteroids << Asteroid.new(x, y) if cell == '#'
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end
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end
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@asteroids
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end
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private
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def parse(text)
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text.lines
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end
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end
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class Asteroid
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attr_reader :x, :y
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def initialize(x, y)
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@x = x
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@y = y
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end
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def neighbors(asteroids)
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by_direction = {}
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asteroids.each do |asteroid|
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next if asteroid == self
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theta = direction_to(asteroid).normalize
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# Since we only care about count, we don't care *which* one we can see at
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# in a given direction. If we do care about it, sort by distance and
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# take the closer one.
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by_direction[theta] = asteroid
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end
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by_direction
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end
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def direction_to(other)
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dx = other.x - x
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dy = other.y - y
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Vector.new(dx, dy)
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end
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def inspect
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"<Asteroid: #{x},#{y}>"
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end
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def to_s
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"(#{x},#{y})"
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end
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end
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class Vector
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attr_reader :x, :y
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def initialize(x, y, normal = false)
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@x = x
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@y = y
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@normal = normal
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end
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def normalize
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return self if @normal
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div = gcd(@x.abs, @y.abs)
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Vector.new(Rational(@x / div), Rational(@y / div), true)
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end
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def ==(other)
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s = normalize
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o = other.normalize
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s.x == o.x && s.y == o.y
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end
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def eql?(other)
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self == other
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end
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def hash
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n = normalize
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[n.x, n.y].hash
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end
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def inspect
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"<Vector: #{x},#{y}>"
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end
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end
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def gcd(n, m)
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# Invariant: n >= m
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n, m = m, n if n < m
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n, m = m, n % m until m.zero?
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n
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end
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belt = AsteroidBelt.new input
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best = belt.asteroids.max_by do |asteroid|
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asteroid.neighbors(belt.asteroids).count
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end
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pp best
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pp best.neighbors(belt.asteroids).count
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