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34
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1 #! /usr/bin/env ruby
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2
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3 if ARGV.length != 1
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4 abort("Incorrect arguments - needs input file")
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5 elsif not File.exist? (ARGV[0])
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6 abort("File #{ARGV[0]} did not exist")
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7 end
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8
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9 file = ARGV[0]
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10
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11 MovingObject = Struct.new(:x, :y, :z, :dx, :dy, :dz)
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12 Position = Struct.new(:x, :y, :z)
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13
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14 box_range = 7..27
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15 box_range = 200000000000000..400000000000000
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16
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17 objects = File.open(file, "r").each_line(chomp: true).map do |line|
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18 pos, vel = line.split(" @ ")
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19 position = pos.split(", ").map(&:to_f)
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20 velocity = vel.split(",").map(&:to_f)
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21 MovingObject.new(position[0], position[1], position[2], velocity[0], velocity[1], velocity[2])
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22 end
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23
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24 # Reset our origin coordinates so that the bounding box starts at 0,0
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25 # This prevents overflow with large numbers in the later calculation
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26 offset = box_range.begin
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27 box_range = 0..(box_range.size-1)
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28 objects.each {|obj| obj.x -= offset; obj.y -= offset; obj.z -= offset}
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29
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30
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31 def is_parallel?(a, b)
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32 (a.dx / b.dx) == (a.dy / b.dy)
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33 end
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34
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35 def is_in_past?(obj, point)
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36 (obj.dx > 0 ? obj.x > point.x : obj.x < point.x) || (obj.dy > 0 ? obj.y > point.y : obj.y < point.y)
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37 end
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38
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39 intersects = objects.combination(2).filter {|a, b| !is_parallel?(a, b) }.map do |a,b|
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40 # https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line
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41 x_1 = a.x
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42 x_2 = a.x + a.dx
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43 x_3 = b.x
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44 x_4 = b.x + b.dx
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45 y_1 = a.y
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46 y_2 = a.y + a.dy
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47 y_3 = b.y
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48 y_4 = b.y + b.dy
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49
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50 px = ((((x_1 * y_2) - (y_1 * x_2)) * (x_3 - x_4)) - ((x_1 - x_2) * ((x_3 * y_4) - (y_3 * x_4)))) / (((x_1 - x_2) * (y_3 - y_4)) - ((y_1 - y_2) * (x_3 - x_4)))
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51 py = ((((x_1 * y_2) - (y_1 * x_2)) * (y_3 - y_4)) - ((y_1 - y_2) * ((x_3 * y_4) - (y_3 * x_4)))) / (((x_1 - x_2) * (y_3 - y_4)) - ((y_1 - y_2) * (x_3 - x_4)))
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52 [a, b, Position.new(px, py, 0)]
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53 end.filter do |a,b,intersect|
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54 box_range.include?(intersect.x) && box_range.include?(intersect.y) && !is_in_past?(a, intersect) && !is_in_past?(b, intersect)
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55 end
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56
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57 puts intersects.length |
