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| require "matrix" | |
| require "set" | |
| # Flood fill from min (up until max) stopping when we hit a cube. | |
| def count_outward_faces(cubes, min, max) | |
| # To avoid stack overflow, we aren't recursive, instead we have a list of squares to check. | |
| to_check = [min] | |
| to_check_set = Set[min] | |
| # Keep track of squares we have tested (as you can get to the same square multiple ways). | |
| visited = Set[] | |
| # Our return. | |
| count = 0 | |
| # From the current cube we go move by the vector below and to a bounds check on the axis index below. | |
| operations = [ | |
| [ Vector[ 1, 0, 0], 0 ], | |
| [ Vector[-1, 0, 0], 0 ], | |
| [ Vector[ 0, 1, 0], 1 ], | |
| [ Vector[ 0, -1, 0], 1 ], | |
| [ Vector[ 0, 0, 1], 2 ], | |
| [ Vector[ 0, 0, -1], 2 ], | |
| ] | |
| while to_check.length > 0 | |
| t = to_check.pop() | |
| to_check_set.delete(t) | |
| visited << t | |
| operations.each { |op| | |
| test = t + op[0] | |
| if test[op[1]] >= min[op[1]] && test[op[1]] <= max[op[1]] | |
| if cubes.include? test | |
| count += 1 | |
| elsif !to_check_set.include?(test) && !visited.include?(test) | |
| to_check << test | |
| to_check_set << test | |
| end | |
| end | |
| } | |
| end | |
| return count | |
| end | |
| def count_all_faces(cubes) | |
| all_faces = {} | |
| cubes.each { |cube| | |
| x0 = cube[0] - 1 | |
| x1 = cube[0] | |
| y0 = cube[1] - 1 | |
| y1 = cube[1] | |
| z0 = cube[2] - 1 | |
| z1 = cube[2] | |
| # Create the 6 faces of this cube. | |
| faces = [ | |
| # Left | |
| [ | |
| Vector[x0, y0, z0], | |
| Vector[x0, y0, z1], | |
| Vector[x0, y1, z1], | |
| Vector[x0, y1, z0], | |
| ], | |
| # Right | |
| [ | |
| Vector[x1, y0, z0], | |
| Vector[x1, y0, z1], | |
| Vector[x1, y1, z1], | |
| Vector[x1, y1, z0], | |
| ], | |
| # Top | |
| [ | |
| Vector[x0, y1, z0], | |
| Vector[x0, y1, z1], | |
| Vector[x1, y1, z1], | |
| Vector[x1, y1, z0], | |
| ], | |
| # Bottom | |
| [ | |
| Vector[x0, y0, z0], | |
| Vector[x0, y0, z1], | |
| Vector[x1, y0, z1], | |
| Vector[x1, y0, z0], | |
| ], | |
| # Front | |
| [ | |
| Vector[x0, y0, z0], | |
| Vector[x0, y1, z0], | |
| Vector[x1, y1, z0], | |
| Vector[x1, y0, z0], | |
| ], | |
| # Back | |
| [ | |
| Vector[x0, y0, z1], | |
| Vector[x0, y1, z1], | |
| Vector[x1, y1, z1], | |
| Vector[x1, y0, z1], | |
| ], | |
| ] | |
| # Our faces are the keys to the dictionary, the value is how many things use that face. | |
| faces.each { |face| | |
| if !all_faces.include? face | |
| all_faces[face] = 1 | |
| else | |
| all_faces[face] += 1 | |
| end | |
| } | |
| } | |
| # We want unique faces, so sum the keys that have a value of 1 (only one cube uses that face). | |
| return all_faces.count { |element| element[1] == 1 } | |
| end | |
| if __FILE__ == $0 | |
| next_dir = 0 | |
| min = Vector[1000000, 1000000, 1000000] | |
| max = Vector[-1000000, -1000000, -1000000] | |
| cubes = Set[] | |
| File.readlines("input.txt").each { |line| | |
| v = line.strip.split(",") | |
| x1 = v[0].to_i | |
| y1 = v[1].to_i | |
| z1 = v[2].to_i | |
| cubes << Vector[x1, y1, z1] | |
| min = Vector[[min[0], x1].min, [min[1], y1].min, [min[2], z1].min] | |
| max = Vector[[max[0], x1].max, [max[1], y1].max, [max[2], z1].max] | |
| } | |
| p1 = count_all_faces(cubes) | |
| puts("Part 1: #{p1}") | |
| p2 = count_outward_faces(cubes, min - Vector[1,1,1], max + Vector[1,1,1]) | |
| puts("Part 2: #{p2}") | |
| end |
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