AdventOfCodeDay3.cs

// part 1

var input = "<input here>";

var visited = new List<Point> { new Point(0, 0) };

var x = 0;
var y = 0;

foreach (var d in input)
{
	if (d == 'v') y--;
	if (d == '>') x++;
	if (d == '^') y++;
	if (d == '<') x--;

	if (!visited.Any(a => a.X == x && a.Y == y))
	{
		visited.Add(new Point(x, y));
	}
}

// part 2

var input = "<input here>";

var visited = new List<Point> { new Point(0, 0) };

var x1 = 0;
var y1 = 0;

var x2 = 0;
var y2 = 0;

var i = 0;
foreach (var d in input)
{
	var x = 0;
	var y = 0;

	if (i % 2 == 0)
	{
		if (d == 'v') y1--;
		if (d == '>') x1++;
		if (d == '^') y1++;
		if (d == '<') x1--;
		x = x1;
		y = y1;
	}
	else
	{
		if (d == 'v') y2--;
		if (d == '>') x2++;
		if (d == '^') y2++;
		if (d == '<') x2--;
		x = x2;
		y = y2;
	}

	if (!visited.Any(a => a.X == x && a.Y == y))
	{
		visited.Add(new Point(x, y));
	}
	i++;
}