#! /usr/bin/env ruby

if ARGV.length != 1
        abort("Incorrect arguments - needs input file")
elsif not File.exist? (ARGV[0])
	abort("File #{ARGV[0]} did not exist")
end

file = ARGV[0]

maps = File.open(file, "r").each_line().map(&:chomp).chunk_while {|before, after| before.length == after.length}.filter {|chunk| chunk != [""]}.map {|chunk| chunk.map{|row| row.each_char.to_a}}

def count_num_changes(row_a, row_b)
	row_a.zip(row_b).map {|a,b| (a != b) ? 1 : 0}.sum
end

def find_imperfect_reflection(data)
	candidate_start = data.each_cons(2).with_index.flat_map {|vals,idx| count_num_changes(*vals) <= 1 ? [idx] : []}
	valid_starts = candidate_start.flat_map do |start|
		pos = start
		reflected = start + 1
		num_changes = count_num_changes(data[pos], data[reflected])
		while pos > 0 and reflected < data.length - 1
			pos -= 1
			reflected += 1
			num_changes_in_row = count_num_changes(data[pos], data[reflected])
			num_changes += num_changes_in_row
			break unless num_changes <= 1
		end
		num_changes == 1 ? [start + 1] : []
	end
	valid_starts[0]
end

puts maps.flat_map {|data| [find_imperfect_reflection(data).to_i * 100, find_imperfect_reflection(data.transpose()).to_i]}.sum