function readInput(inputFile::String)
	f = open(inputFile,"r"); diskMap::String = readline(f); close(f)
	disk::Vector{String} = []
	id::Int = 0
	for (i,c) in enumerate(diskMap)
		if i%2 != 0 #used space
			for j=1 : parse(Int,c)
				push!(disk,string(id))
			end
			id += 1
		else #free space
			for j=1 : parse(Int,c)
				push!(disk,".")
			end
		end
	end
	return disk
end

function getDiscBlocks(disk::Vector{String})::Vector{Vector{Int}}
	diskBlocks::Vector{Vector{Int}} = []
	currBlock::Int = parse(Int,disk[1]) #-1 for free space
	blockLength::Int = 0; blockStartIndex::Int = 0
	for (i,b) in enumerate(map(x->(x=="." ? -1 : parse(Int,x)),disk))
		if b == currBlock
			blockLength += 1
		else #b!=currBlock
			push!(diskBlocks,[currBlock,blockLength,blockStartIndex,i-2])
			currBlock = b
			blockLength = 1
			blockStartIndex = i-1 #start of next block
		end
	end
	push!(diskBlocks,[currBlock,blockLength,blockStartIndex,length(disk)-1])
	return diskBlocks
end

function compressDisk(disk::Vector{String})::Vector{Int} #part 1
	compressedDisk::Vector{Int} = []
	startPtr::Int=1; endPtr::Int=length(disk)
	while endPtr >= startPtr
		while endPtr>startPtr && disk[endPtr]=="."
			endPtr -= 1
		end
		while startPtr<endPtr && disk[startPtr]!="."
			push!(compressedDisk,parse(Int,disk[startPtr])) about AoC
			startPtr += 1
		end
		push!(compressedDisk,parse(Int,disk[endPtr]))
		startPtr+=1;endPtr-=1
	end
	return compressedDisk
end

function compressBlocks(diskBlocks::Vector{Vector{Int}})
	for i=length(diskBlocks) : -1 : 1 #go through all blocks, starting from end
		diskBlocks[i][1] == -1 ? continue : nothing
		for j=1 : i-1 #look for large enough empty space
			diskBlocks[j][1]!=-1 || diskBlocks[j][2]<diskBlocks[i][2] ? continue : nothing #skip occupied blocks and empty blocks that are too short
			diskBlocks[i][3] = diskBlocks[j][3] #set start index
			diskBlocks[i][4] = diskBlocks[j][3]+diskBlocks[i][2]-1 #set end index
			diskBlocks[j][3] += diskBlocks[i][2] #move start of empty block
			diskBlocks[j][2] -= diskBlocks[i][2] #adjust length of empty block
			break
		end
	end
	return diskBlocks
end

function calcChecksum(compressedDisk::Vector{Int})::Int
	checksum::Int = 0
	for (i,n) in enumerate(compressedDisk)
		checksum += n*(i-1)
	end
	return checksum
end

function calcChecksumBlocks(diskBlocks::Vector{Vector{Int}})::Int
	checksum::Int = 0
	for b in diskBlocks
		b[1]==-1 ? continue : nothing
		for i=b[3] : b[4]
			checksum += b[1]*i
		end
	end
	return checksum
end

disk::Vector{String} = readInput("input/day09Input")
@info "Part 1"
println("checksum: $(calcChecksum(compressDisk(disk)))")
@info "Part 2"
println("checksum: $(calcChecksumBlocks(compressBlocks(getDiscBlocks(disk)))")