this post was submitted on 08 Dec 2024
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Advent Of Code

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๐Ÿ›œ - 2024 DAY 8 SOLUTIONS -๐Ÿ›œ (programming.dev)
submitted 2 weeks ago by [email protected] to c/[email protected]
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Day 8: Resonant Collinearity

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[โ€“] [email protected] 2 points 2 weeks ago

Julia

I was surprised when my solution worked for part 2 since I thought you also had to include fractions of antenna distances, but apparently not.

Code

function readInput(inputFile::String)::Matrix{Char}
	f = open(inputFile,"r")
	lines::Vector{String} = readlines(f)
	close(f)
	cityMap = Matrix{Char}(undef,length(lines),length(lines[1]))
	for (i,l) in enumerate(lines)
		cityMap[i,:] = collect(l)
	end
	return cityMap
end

function getAntennaLocations(cityMap::Matrix{Char})::Dict
	antennaLocations = Dict{Char,Vector{Vector{Int}}}()
	for l=1 : size(cityMap)[1]
		for c=1 : size(cityMap)[2]
			cityMap[l,c]=='.' ? continue : nothing
			if !haskey(antennaLocations,cityMap[l,c])
				antennaLocations[cityMap[l,c]] = []
			end
			push!(antennaLocations[cityMap[l,c]],[l,c])
		end
	end
	return antennaLocations
end

function countAntinodes(cityMap::Matrix{Char},antLoc::Dict{Char,Vector{Vector{Int}}},withHarmonics::Bool)::Int #antLoc: antenna locations
	lBounds = 1:size(cityMap)[1]; cBounds = 1:size(cityMap)[2]
	anodeLocs::Matrix{Bool} = zeros(size(cityMap))
	for key in keys(antLoc)
		for i=1 : length(antLoc[key])
			withHarmonics&&length(antLoc[key])>1 ? anodeLocs[antLoc[key][i][1],antLoc[key][i][2]]=1 : nothing #add antenna locations as antinodes
			#should also add fractions of antenna distances, but works without
			for j=i+1 : length(antLoc[key])
				harmonic::Int = 1
				while true
					n1l = antLoc[key][i][1]+harmonic*(antLoc[key][i][1]-antLoc[key][j][1])
					n1c = antLoc[key][i][2]+harmonic*(antLoc[key][i][2]-antLoc[key][j][2])
					n2l = antLoc[key][j][1]+harmonic*(antLoc[key][j][1]-antLoc[key][i][1])
					n2c = antLoc[key][j][2]+harmonic*(antLoc[key][j][2]-antLoc[key][i][2])
					if n1l in lBounds && n1c in cBounds
						anodeLocs[n1l,n1c] = 1
					end
					if n2l in lBounds && n2c in cBounds
						anodeLocs[n2l,n2c] = 1
					end
					withHarmonics ? nothing : break
					!(n1l in lBounds) && !(n1c in cBounds) && !(n2l in lBounds) && !(n2c in cBounds) ? break : harmonic+=1
				end
			end
		end
	end
	return sum(anodeLocs)
end

@info "Part 1"
println("antinode count $(countAntinodes(getAntennaLocations(readInput("day08Input"))),false)")
@info "Part 2"
println("antinode count $(countAntinodes(getAntennaLocations(readInput("day08Input"))),faltrue)")