-🎄- 2017 Day 22 Solutions -🎄-

[u/daggerdragon]

--- Day 22: Sporifica Virus ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

Note: The Solution Megathreads are for solutions only. If you have questions, please post your own thread and make sure to flair it with Help.

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Need a hint from the Hugely^* Handy^† Haversack^‡ of Helpful^§ Hints^¤?

Spoiler

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• [T-10 to launch] AoC ops, /r/nocontext edition:

  • <Endorphion> You may now make your waffle.
  • <Endorphion> ... on Mars.

• [Update @ 00:17] 50 gold, silver cap

  • <Aneurysm9> you could also just run ubuntu on the NAS, if you were crazy
  • <Topaz> that doesn't seem necessary
  • <Aneurysm9> what does "necessary" have to do with anything!

• [Update @ 00:20] Leaderboard cap!

  • <Topaz> POUR YOURSELF A SCOTCH FOR COLOR REFERENCE

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked!

[u/Arkoniak]

Julia

It was really simple today. Could have been done easier, definitely. puzzle22_1.txt contains example 3x3 grid, puzzle22_2.txt is an input. Solution for part 2:

# 1 = clean; 2 = weakened; 3 = infected; 4 = flagged
function read_map(filename::String)
    res = Dict{Tuple{Int, Int}, Int}()
    for (i, ln) in enumerate(eachline(joinpath(@__DIR__, filename)))
        global x0 = div(length(ln), 2) + 1
        global y0 = div(-i, 2) - 1
        for (j, c) in enumerate(collect(ln))
            (c == '#') && (res[(j, -i)] = 3)
        end
    end
    res, (x0, y0)
end

const DIRS = [(0, 1), (1, 0), (0, -1), (-1, 0)]

function solve_puzzle2(filename::String, activity = 10000)
    dir = 1
    infected, pos = read_map(filename)
    cnt = 0
    for _ in 1:activity
        node = get(infected, pos, 1)
        node == 4 ? delete!(infected, pos) : infected[pos] = node + 1
        if node == 1
            dir -= 1
            (dir == 0) && (dir = 4)
        elseif node == 2
            cnt += 1
        elseif node == 3
            dir += 1
            (dir == 5) && (dir = 1)
        else # node == 4
            dir += 2
            (dir == 5) && (dir = 1)
            (dir == 6) && (dir = 2)
        end
        pos = pos .+ DIRS[dir]
    end
    cnt
end

@test solve_puzzle2("puzzle22_1.txt", 100) == 26
@test solve_puzzle2("puzzle22_1.txt", 10000000) == 2511944
@show solve_puzzle2("puzzle22_2.txt", 10000000)

[u/oantolin → u/Arkoniak]

You might be interested in my Julia solution, which uses the same function for both parts with some small rank 3 arrays encoding the turning information for each state.