[2023] Day15

Author: lambda-mike

.github/workflows/2023-julia.yaml

@@ -27,4 +27,5 @@ jobs:
         julia day07.jl
         julia day08.jl
         julia day09.jl
+        julia day15.jl
 

2023/day15.jl

@@ -0,0 +1,92 @@
+abstract type Instruction end
+
+struct Add <: Instruction
+    label::String
+    len::Int
+end
+
+struct Rem <: Instruction
+    label::String
+end
+
+function calcHash(str::AbstractString)::Int
+    result = 0
+    for c in str
+        result += Int(c)
+        result *= 17
+        result = result % 256
+    end
+    result
+end
+
+function solveA(input)
+    steps = split(input, ",")
+    [ calcHash(s) for s in steps ] |> sum
+end
+
+function parseStep(str)::Instruction
+    if str[end] == '-'
+        return Rem(join(str[1:end-1]))
+    else
+        label = str[1:end - 2]
+        len = parse(Int, str[end])
+        return Add(join(label), len)
+    end
+end
+
+function placeLensInBoxes!(hashmap::Dict{String, Int}, instructions::Vector{Instruction}, boxes::Vector{Vector{Add}})
+    for instruction in instructions
+        n = hashmap[instruction.label]
+        box = boxes[n + 1]
+        i = findfirst(x -> x.label == instruction.label, box)
+        if instruction isa Add
+            if i === nothing
+                push!(box, instruction)
+            else
+                box[i] = instruction
+            end
+        else # Rem
+            i !== nothing &&  deleteat!(box, i)
+        end
+    end
+end
+
+calculateFocusingPower(box::Int, slot::Int, len::Int) = box * slot * len
+
+function solveB(input)
+    boxesN = 256
+    steps = split(input, ",")
+    instructions = [ parseStep(s) for s in steps ]
+    hashmap = Dict([ (i.label, calcHash(i.label)) for i in instructions ])
+    boxes::Vector{Vector{Add}} = repeat([Vector{Add}[]], boxesN)
+    placeLensInBoxes!(hashmap, instructions, boxes)
+    result = 0
+    for b in 1:boxesN
+        for (i, lens) in enumerate(boxes[b])
+            result += calculateFocusingPower(b, i, lens.len)
+        end
+    end
+    return result
+end
+
+function main(file = "day15.txt")
+    # input = collect(eachline(file))
+    input = strip(read(file, String))
+    # 495972
+    println("Solving Day15A...")
+    println(solveA(input))
+    # 245223
+    println("Solving Day15B...")
+    println(solveB(input))
+end
+
+if !isinteractive()
+    main()
+end
+
+function repl()
+    # file = "day15s.txt"
+    file = "day15.txt"
+    println("file: $file")
+    main(file)
+end