Julia

No really proud of todays solution. Probably because I started too late today.

I used a dictionary with the numbers that should be in front of any given number. Then I checked if they appear after that number. Part1 check. For part 2 I just hoped for the best that ordering it would work by switching each two problematic entries and it worked.

::: spoiler

function readInput(inputFile::String)
	f = open(inputFile,"r"); lines::Vector{String} = readlines(f); close(f)
	updates::Vector{Vector{Int}} = []
	pageOrderingRules = Dict{Int,Vector{Int}}()
	readRules::Bool = true #switch off after rules are read, then read updates
	for (i,line) in enumerate(lines)
		line=="" ? (readRules=false;continue) : nothing
		if readRules
			values::Vector{Int} = map(x->parse(Int,x),split(line,"|"))
			!haskey(pageOrderingRules,values[2]) ? pageOrderingRules[values[2]]=Vector{Int}() : nothing
			push!(pageOrderingRules[values[2]],values[1])
		else #read updates
			push!(updates,map(x->parse(Int,x),split(line,",")))
		end
	end
	return updates, pageOrderingRules
end

function checkUpdateInOrder(update::Vector{Int},pageOrderingRules::Dict{Int,Vector{Int}})::Bool
	inCorrectOrder::Bool = true
	for i=1 : length(update)-1
		for j=i+1 : length(update)
			!haskey(pageOrderingRules,update[i]) ? continue : nothing
			update[j] in pageOrderingRules[update[i]] ? inCorrectOrder=false : nothing
		end
		!inCorrectOrder ? break : nothing
	end
	return inCorrectOrder
end

function calcMidNumSum(updates::Vector{Vector{Int}},pageOrderingRules::Dict{Int,Vector{Int}})::Int
	midNumSum::Int = 0
	for update in updates
		checkUpdateInOrder(update,pageOrderingRules) ? midNumSum+=update[Int(ceil(length(update)/2))] : nothing
	end
	return midNumSum
end

function calcMidNumSumForCorrected(updates::Vector{Vector{Int}},pageOrderingRules::Dict{Int,Vector{Int}})::Int
	midNumSum::Int = 0
	for update in updates
		inCorrectOrder::Bool = checkUpdateInOrder(update,pageOrderingRules)
		inCorrectOrder ? continue : nothing #skip already correct updates
		while !inCorrectOrder
			for i=1 : length(update)-1
				for j=i+1 : length(update)
					!haskey(pageOrderingRules,update[i]) ? continue : nothing
					if update[j] in pageOrderingRules[update[i]]
						mem::Int = update[i]; update[i] = update[j]; update[j]=mem #switch entries
					end
				end
			end
			inCorrectOrder = checkUpdateInOrder(update,pageOrderingRules)
		end
		midNumSum += update[Int(ceil(length(update)/2))]
	end
	return midNumSum
end

updates, pageOrderingRules = readInput("day05Input")
println("part 1 sum: $(calcMidNumSum(updates,pageOrderingRules))")
println("part 2 sum: $(calcMidNumSumForCorrected(updates,pageOrderingRules))")

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