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#!/usr/bin/env ruby
def turn_left(vector)
return case vector
when [1, 0]
[0, 1]
when [0, 1]
[-1, 0]
when [-1, 0]
[0, -1]
when [0, -1]
[1, 0]
end
end
def turn_right(vector)
return case vector
when [1, 0]
[0, -1]
when [0, -1]
[-1, 0]
when [-1, 0]
[0, 1]
when [0, 1]
[1, 0]
end
end
input = $stdin.readlines.map(&:chomp)
size = input.length
infinity = 1000
map = []
infinity.times do
map << ([:clean]*((2*infinity)+size))
end
input.each do |r|
map << ([:clean]*infinity) + r.chars.map{|x| x == '#' ? :infected : :clean} + ([:clean]*infinity)
end
infinity.times do
map << ([:clean]*((2*infinity)+size))
end
row = infinity + (size + 1)/2 - 1
col = infinity + (size + 1)/2 - 1
dir = [-1, 0]
infections = 0
10_000_000.times do
case map[row][col]
when :clean
dir = turn_left(dir)
map[row][col] = :weakened
when :weakened
map[row][col] = :infected
infections += 1
when :infected
dir = turn_right(dir)
map[row][col] = :flagged
when :flagged
dir = turn_right(turn_right(dir))
map[row][col] = :clean
end
row += dir[0]
col += dir[1]
end
puts infections
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