DEV Community

Caleb Weeks
Caleb Weeks

Posted on

Advent of Code #13 (in Crystal)

Similar to yesterday's puzzle, this one was fairly easy to visually inspect, but requires a bit more work to describe algorithmically. Not quite a bad as yesterday, though.

For part 1, I originally took the two halves on either side of each row, reversed one of them and then compared the two using the equality comparison (==). It was easy enough to swap out that equality comparison for a Levenshtein distance, which Crystal conveniently provides in the standard library.

There is still a fair amount of code duplication between parts 1 and 2, but I didn't feel like refactoring it much today.

Here's the code:

require "levenshtein"

input = File.read("input").strip

patterns = input.split("\n\n")

def find_mirror(rows, distance = 0)
  mirror = 0
  (1...rows.size).each do |i|
    edge = Math.min(i, rows.size - i)
    image = rows[i - edge...i].join
    reflection = rows[i...i + edge].reverse.join
    mirror = i if Levenshtein.distance(image, reflection) == distance
  end
  mirror
end

part1 = patterns.reduce(0) do |sum, pattern|
  rows = pattern.split("\n")
  cols = Array.new(rows[0].size, "")
  rows.each do |row|
    row.each_char.with_index do |char, col|
      cols[col] += char
    end
  end
  sum + find_mirror(rows) * 100 + find_mirror(cols)
end

puts part1

part2 = patterns.reduce(0) do |sum, pattern|
  rows = pattern.split("\n")
  cols = Array.new(rows[0].size, "")
  rows.each do |row|
    row.each_char.with_index do |char, col|
      cols[col] += char
    end
  end
  sum + find_mirror(rows, 1) * 100 + find_mirror(cols, 1)
end

puts part2
Enter fullscreen mode Exit fullscreen mode

AWS Security LIVE!

Tune in for AWS Security LIVE!

Join AWS Security LIVE! for expert insights and actionable tips to protect your organization and keep security teams prepared.

Learn More

Top comments (0)

Billboard image

The Next Generation Developer Platform

Coherence is the first Platform-as-a-Service you can control. Unlike "black-box" platforms that are opinionated about the infra you can deploy, Coherence is powered by CNC, the open-source IaC framework, which offers limitless customization.

Learn more

👋 Kindness is contagious

Please leave a ❤️ or a friendly comment on this post if you found it helpful!

Okay