public void Part1()
{
InitGrid();
// start in the middle
IntCode intCode = new IntCode("Day11", Instructions);
Robot robot = new Robot(intCode, Grid, 0);
List <Task> tasks = new List <Task>();
// this block doesn't like to be put in a loop - channel sync crashes
tasks.Add(Task.Run(() => { intCode.RunIntCode(); }));
tasks.Add(Task.Run(() => { robot.Run(); }));
Task.WaitAll(tasks.ToArray());
int rslt = robot.ChangeCount;
Console.WriteLine("Part1 {0}", rslt);
}