Diagnostics indicate that the local grid computing cluster has been contaminated with the Sporifica Virus. The grid computing cluster is a seemingly-infinite two-dimensional grid of compute nodes. Each node is either clean or infected by the virus.

Read the full puzzle.

using System;
using System.Collections.Generic;

namespace AdventOfCode.Y2017.Day22;

enum State {
    Clean,
    Weakened,
    Infected,
    Flagged
}

[ProblemName("Sporifica Virus")]
class Solution : Solver {

    public object PartOne(string input) =>
        Iterate(input, 10000,
            (state, drow, dcol) =>
                state switch {
                    State.Clean => (State.Infected, -dcol, drow),
                    State.Infected => (State.Clean, dcol, -drow),
                    _ => throw new ArgumentException()
                }
        );

    public object PartTwo(string input) =>
        Iterate(input, 10000000,
            (state, drow, dcol) =>
                state switch {
                    State.Clean => (State.Weakened, -dcol, drow),
                    State.Weakened => (State.Infected, drow, dcol),
                    State.Infected => (State.Flagged, dcol, -drow),
                    State.Flagged => (State.Clean, -drow, -dcol),
                    _ => throw new ArgumentException()
                }
        );


    int Iterate(string input, int iterations, Func<State, int, int, (State State, int irow, int icol)> update) {
        var lines = input.Split('\n');
        var crow = lines.Length;
        var ccol = lines[0].Length;
        var cells = new Dictionary<(int irow, int icol), State>();
        for (int irowT = 0; irowT < crow; irowT++) {
            for (int icolT = 0; icolT < ccol; icolT++) {
                if (lines[irowT][icolT] == '#') {
                    cells.Add((irowT, icolT), State.Infected);
                }
            }
        }
        var (irow, icol) = (crow / 2, ccol / 2);
        var (drow, dcol) = (-1, 0);
        var infections = 0;
        for (int i = 0; i < iterations; i++) {
            var state = cells.TryGetValue((irow, icol), out var s) ? s : State.Clean;

            (state, drow, dcol) = update(state, drow, dcol);

            if (state == State.Infected) {
                infections++;
            }
            if (state == State.Clean) {
                cells.Remove((irow, icol));
            } else {
                cells[(irow, icol)] = state;
            }
            (irow, icol) = (irow + drow, icol + dcol);
        }
        return infections;
    }
}

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