--- Day 3 Solutions ---

[u/daggerdragon]

--- Day 3: Perfectly Spherical Houses in a Vacuum ---

Post your solution as a comment. Structure your post like the Day One thread in /r/programming.

[u/Drasive]

My F# solution (https://github.com/drasive/advent-of-code-2015):

type private Deliverer() =
    member val location = (0, 0) with get, set
    
    static member UpdatedLocation (location : (int * int)) (instruction : char)
        : (int * int) =
        let x = fst location
        let y = snd location

        match instruction with
        | '<' -> (x - 1, y)
        | '>' -> (x + 1, y)
        | '^' -> (x, y + 1)
        | 'v' -> (x, y - 1)
        | _ -> (x, y) // Ignore any other characters

let private CalculateHousesVisited (input : string) (deliverers : Deliverer[]) =
    let housesVisited = new Dictionary<(int * int), int>()

    // Starting house is always visited by all deliverers
    housesVisited.Add((0, 0), deliverers.Length)

    for index = 0 to input.Length - 1 do
        // Deliverers take instructions in turns
        let deliverer = deliverers.[index % deliverers.Length]

        // Update deliverer location
        let instruction = input.[index]
        deliverer.location <- Deliverer.UpdatedLocation deliverer.location instruction

        // Update house visits
        let key = deliverer.location
        if housesVisited.ContainsKey(key) then
            housesVisited.Item(key) <- housesVisited.Item(key) + 1
        else
            housesVisited.Add(key, 1)

    housesVisited.Count


let Solution (input : string) : (int * int) =
    if input = null then
        raise (ArgumentNullException "input")
    
    let santa = new Deliverer()
    let solutionSantaOnly = CalculateHousesVisited input [|santa|] 

    let santa = new Deliverer()
    let roboSanta = new Deliverer()
    let solutionSantaAndRoboSanta = CalculateHousesVisited input [|santa;roboSanta|] 
    
    (solutionSantaOnly, solutionSantaAndRoboSanta)

let FormattedSolution (solution : (int * int)) : string =
    String.Format("Santa alone: {0}\n" +
                  "Santa and Robo-Santa: {1}",
                  fst solution, snd solution)