AdventOfCode-2020/day5.cr

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2020-12-04 21:32:28 -08:00
INPUT = File.read("day5.txt").lines.map(&.chomp)
def partition(choices, list)
b = 0
e = list.size
choices.chars.each do |c|
b = (b+e)//2 if c == 'B' || c == 'R'
e = (b+e)//2 if c == 'F' || c == 'L'
end
return {b,e}
end
def get_id(str)
col = str[0..6]
row = str[7..]
{partition(col, (0..127).to_a)[0], partition(row, (0..7).to_a)[0]}
end
def id(t)
r, c = t
r * 8 + c
end
def part1
input = INPUT.clone
max = input.max_of do |line|
r, c = get_id(line)
r * 8 + c
end
puts max
end
def part2
input = INPUT.clone
seen = Set(Int32).new
max = input.each do |line|
seen << id(get_id(line))
end
candidates = [] of Int32
128.times do |r|
next if r == 0 || r == 127
8.times do |c|
next if seen.includes? id({r, c})
candidates << id({r,c})
end
end
candidates = candidates.select do |i|
seen.includes?(i-1) && seen.includes?(i+1)
end
puts candidates[0]
end
part1
part2