Day 3: Mull It Over
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5 points
I started poking at doing a proper lexer/parser, but then I thought about how early in AoC it is and how low the chance is that the second part will require proper parsing.
So therefore; hello regex my old friend, I’ve come to talk with you again.
C#
List<string> instructions = new List<string>();
public void Input(IEnumerable<string> lines)
{
foreach (var line in lines)
instructions.AddRange(Regex.Matches(line, @"mul\(\d+,\d+\)|do\(\)|don't\(\)").Select(m => m.Value));
}
public void Part1()
{
var sum = instructions.Select(mul => Regex.Match(mul, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value))).Select(cc => cc.Aggregate(1, (acc, val) => acc * val)).Sum();
Console.WriteLine($"Sum: {sum}");
}
public void Part2()
{
bool enabled = true;
long sum = 0;
foreach(var inst in instructions)
{
if (inst.StartsWith("don't"))
enabled = false;
else if (inst.StartsWith("do"))
enabled = true;
else if (enabled)
sum += Regex.Match(inst, @"(\d+),(\d+)").Groups.Values.Skip(1).Select(g => int.Parse(g.Value)).Aggregate(1, (acc, val) => acc * val);
}
Console.WriteLine($"Sum: {sum}");
}
