AdventOfCode-2020/day20.cr

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require "advent"
tiles = input(2020, 20).split "\n\n"
tiles.pop
thash = {} of Int32 => Array(Array(Char))
tiles = tiles.map do |t|
tl = t.lines
tid = tl[0].match(/Tile (\d+):/).not_nil![1].to_i32
tls = tl[1..]
thash[tid] = tls.map &.chars
end
class Array(T)
def matches?(other)
zip_with(other) { |l,r| l == r }.all?
end
def rotate
reverse.transpose
end
end
def check(side_a, side_b)
return :normal if side_a.matches?(side_b)
return :flip if side_a.matches?(side_b.reverse)
return nil
end
def check_all(side_a, other, other_t)
check(side_a, other.first) || check(side_a, other.last) || check(side_a, other_t.first) || check(side_a, other_t.last)
end
MONSTER = [ {0, 1}, {1, 0}, {4, 0}, {5, 1}, {6, 1}, {7, 0}, {10, 0}, {11,1}, {12, 1}, {13, 0}, {16, 0},
{17, 1}, {18, 1}, {18, 2}, {19, 1} ]
def stitch(m, thash, corner)
image = Array(Array(Char)).new(12*8) do |y|
Array(Char).new(12*8) do |x|
'.'
end
end
tile = thash[corner]
tile_id = corner
tile.reverse! if m[corner].has_key? :top
tile.each &.reverse! if m[corner].has_key? :left
12.times do |row|
tile = tile.not_nil!
row_tile = tile
row_id = tile_id
12.times do |col|
row_tile = row_tile.not_nil!
(0..7).each do |y|
(0..7).each do |x|
image[col*8+y][row*8+x] = row_tile[y+1][x+1]
end
end
matches = nil
thash.each do |other_id, other_tile|
next if matches
next if other_id == row_id
4.times do
if row_tile.last.matches? other_tile.first
row_id = other_id
matches = other_tile
elsif row_tile.last.matches? other_tile.first.reverse
row_id = other_id
matches = other_tile.map &.reverse
end
other_tile = other_tile.rotate
end
end
row_tile = matches
end
rot = tile.rotate
matches = nil
thash.each do |other_id, other_tile|
next if matches
next if other_id == tile_id
4.times do
if rot.last.matches? other_tile.first
tile_id = other_id
matches = other_tile.rotate.rotate.rotate
elsif rot.last.matches? other_tile.first.reverse
tile_id = other_id
matches = other_tile.map(&.reverse).rotate.rotate.rotate
end
other_tile = other_tile.rotate
end
end
tile = matches
end
image
end
def find_dragons(stitch)
dragons = [] of {Int32,Int32}
stitch.each_with_index do |row, y|
row.each_with_index do |c, x|
is_dragon = MONSTER.all? do |dx, dy|
(stitch[y+dy]?.try &.[x+dx]?) == '#'
end
dragons << {x,y} if is_dragon
end
end
dragons
end
def find_all_dragons(stitch)
dragons = [] of {Int32,Int32}
4.times do
dragons.concat find_dragons(stitch)
dragons.concat find_dragons(stitch.reverse)
stitch = stitch.rotate
end
dragons
end
def match(thash, tile)
matches = {} of Symbol => {Int32, Symbol}
cs = thash[tile]
tcs = cs.transpose
thash.each do |t, ocs|
next if t == tile
tocs = ocs.transpose
top = check_all(cs.first, ocs, tocs)
bottom = check_all(cs.last, ocs, tocs)
left = check_all(tcs.first, ocs, tocs)
right = check_all(tcs.last, ocs, tocs)
matches[:top] = {t, top} if top
matches[:left] = {t, left} if left
matches[:bottom] = {t, bottom} if bottom
matches[:right] = {t, right} if right
end
matches
end
def part1(input)
corners = input.select do |t, i|
match(input, t).size == 2
end
corners.keys.map(&.to_i64).product
end
def part2(input)
matches = {} of Int32 => Hash(Symbol, {Int32, Symbol})
corners = input.select do |t, i|
matches[t] = match(input, t)
match(input, t).size == 2
end
stitched = stitch(matches, input, corners.first[0])
dragons = find_all_dragons(stitched)
stitched.sum(&.count(&.==('#'))) - (dragons.size * MONSTER.size)
end
puts part1(thash.clone)
puts part2(thash.clone)