AOC 2020 Day 13

#load "xunit"
#load "..\AOC Connector"

void Main(string[] args)
{
    if(args == null)
        RunTests();  // Call RunTests() or press Alt+Shift+T to initiate testing.

    //get aoc data
    var aoc = new AdventOfCode(2020, 13);

    //solve A
    aoc.SubmitAnswer(SolveA(aoc.InputLines), Part.A);

    //solve B
    aoc.SubmitAnswer(SolveB(aoc.InputLines), Part.B);
}



int SolveA(string[] data)
{
    int time = int.Parse(data[0]);
    var firstBus = data[1].Split(',')
        .Where(x => x != "x") //split remove empty
        .Select(x => int.Parse(x)) //get ints
        .Select(x => (bus: x, minTillNext: x - (time % x)))
        .OrderBy(x => x.minTillNext)
        .First();



    return firstBus.minTillNext * firstBus.bus;
}
ulong SolveB(string[] data)
{
    //create a list with the busses and theid offsets
    var buses = data[1].Split(',')
        .Select((x, i) => (x, i))
        .Where(x => x.x != "x")
        .Select(item => new { bus = ulong.Parse(item.x), offset = (ulong) item.i})
        .ToList();

    //list with the available busses
    var allBuses = buses.ToList();

    //track the time and stepsize
    ulong time = 0;
    ulong stepSize = 1;

    //loop through th e
    while (buses.Count > 0)
    {
        //increment the time with the stepsize
        time += stepSize;

        //is this the point where the busses are in sync
        if((time + buses[0].offset) % buses[0].bus == 0)
        {
            //multiple the stepsize with the current step
            stepSize *= buses[0].bus;
            //remove this bus
            buses.RemoveAt(0);
        }

    }

    //done
    return time;
}


// You can define other methods, fields, classes and namespaces here

#region private::Tests
//test data
string[] testdata = new[]
{
"939",
"7,13,x,x,59,x,31,19"
};

//tests
[Fact] void TestA() => Assert.Equal(295, SolveA(testdata));
[Fact] void TestB() => Assert.Equal((ulong)1068781, SolveB(testdata));

#endregion