Day 20

1 files changed, 102 insertions, 0 deletions

diff --git a/day20/part2 b/day20/part2
new file mode 100755
index 0000000..1d474e1
--- /dev/null
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@@ -0,0 +1,102 @@
+#!/usr/bin/env ruby
+
+require 'scanf'
+
+class Array
+  def find_all_indices(elt)
+    return self.each_index.select { |i| self[i] == elt }
+  end
+end
+
+class Vector
+  attr_accessor :x, :y, :z
+
+  def initialize(array)
+    @x = array[0] || 0
+    @y = array[1] || 0
+    @z = array[2] || 0
+  end
+
+  def add!(vector)
+    @x += vector.x
+    @y += vector.y
+    @z += vector.z
+  end
+
+  def to_s
+    return "<#{@x},#{@y},#{@z}>"
+  end
+end
+
+class Particle
+  attr_accessor :pos, :vel, :acc
+
+  def initialize(p, v, a)
+    @pos = Vector.new(p)
+    @vel = Vector.new(v)
+    @acc = Vector.new(a)
+    @destroyed = false
+  end
+
+  def destroy!
+    @destroyed = true
+  end
+
+  def destroyed?
+    return @destroyed
+  end
+
+  def collides?(other)
+    return @pos.x == other.pos.x &&
+           @pos.y == other.pos.y &&
+           @pos.z == other.pos.z
+  end
+
+  def update!
+    @vel.add!(@acc)
+    @pos.add!(@vel)
+  end
+
+  def to_s
+    return "p=#{@pos}, v=#{@vel}, a=#{@acc}"
+  end
+end
+
+input = $stdin.readlines.map(&:chomp)
+
+particles = input.map do |line|
+  px, py, pz, vx, vy, vz, ax, ay, az = 
+    line.scanf("p=<%d,%d,%d>, v=<%d,%d,%d>, a=<%d,%d,%d>")
+  Particle.new([px, py, pz], [vx, vy, vz], [ax, ay, az])
+end
+
+times = 0
+
+THE_LONG_RUN = 1000
+
+loop do
+  collision = false
+
+  (0...particles.length).each do |i|
+    (i+1...particles.length).each do |j|
+      if particles[i].collides?(particles[j]) then
+        collision = true
+        particles[i].destroy!
+        particles[j].destroy!
+      end
+    end
+  end
+
+  if !collision then
+    times += 1
+  else
+    times = 0
+  end
+
+  break if times == THE_LONG_RUN
+
+  particles.each(&:update!)
+  particles = particles.reject(&:destroyed?)
+end
+
+p particles.length