Day3.cs

var file = @"d:\code\decriptor\input3.txt";

var input = File.ReadLines(file).ToArray();

var priority = 0;
var badgePriority = 0;
for(int i = 0; i < input.Count(); i += 3)
{
	var input1 = input[i];
	var input2 = input[i+1];
	var input3 = input[i+2];

	priority += GetCharValue(FindCommonItem(SplitString(input1)));
	priority += GetCharValue(FindCommonItem(SplitString(input2)));
	priority += GetCharValue(FindCommonItem(SplitString(input3)));

	var badge = input1
				.Intersect(input2)
				.Intersect(input3)
				.First();

	badgePriority += GetCharValue(badge);
}

IEnumerable<char>[] SplitString(string input)
{
	var half = input.Length / 2;
	var first = input.Take(half);
	var second = input.TakeLast(half);

	return new[] { first, second };
}

char FindCommonItem (IEnumerable<char>[] parts)
{
	return parts[0].Intersect(parts[1]).First();
}

int GetCharValue(char item)
{
	if (Char.IsLower(item))
		return (int)item - 96;

	return(int)item - 38;
}