Day 8: Haunted Wasteland

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

FAQ

  • @[email protected]
    2•1 year ago

    Crystal

    [email protected]

    part 1 was made way simpler after I made it a function for part 2
    also I accidentally saw someone elses code, so I can’t take full credit for figuring out how to do part 2

    Input = File.read("input.txt").lines

Dirs = Input[0].chars.map {|c| c == 'L' ? 0 : 1}
Nodes = Hash(String, Tuple(String, String)).new
Input[2..].each {|line| Nodes[line[..2]] = {line[7..9], line[12..14]} }

# part 1
puts num_steps("AAA", &.== "ZZZ")

# part 2
currents = Nodes.keys.select(&.ends_with? 'A')
steps = currents.map {|cur| num_steps(cur, &.ends_with? 'Z')}
puts steps.reduce(1_i64) {|a, b| a.lcm b}

def num_steps(start)
	steps = 0
	Dirs.cycle do |dir|
		steps += 1
		start = Nodes[start][dir]
		break if yield start
	end
	steps
end