private static void SolvePart2(Dictionary <int, Rule> rules, string[] messages)
{
// 0: 8 11
// 8: 42 | 42 8
// 11: 42 31 | 42 11 31
Rule rule42 = rules[42];
Rule rule31 = rules[31];
HashSet <string> rule42Map = rule42.Permutations;
HashSet <string> rule31Map = rule31.Permutations;
int matches = 0;
Console.WriteLine($"messages = {messages.Length}, <=24 {messages.Count(x => x.Length <= 24)}, >24 {messages.Count(x => x.Length > 24)}");
foreach (string message in messages)
{
// if we start at the end and go down until we don't match 31
if (!rule42Map.Contains(message.Substring(0, 8)) ||
!rule42Map.Contains(message.Substring(8, 8)))
{
continue;
}
if (!rule31Map.Contains(message.Substring(message.Length - 8, 8)))
{
continue;
}
int minRequired42 = 0;
int currentIndex = message.Length - 8;
while (currentIndex > (16 + minRequired42 * 8))
{
if (!rule31Map.Contains(message.Substring(currentIndex - 8, 8)))
{
break;
}
minRequired42++;
currentIndex -= 8;
}
bool match = true;
while (currentIndex > 16)
{
if (!rule42Map.Contains(message.Substring(currentIndex - 8, 8)))
{
match = false;
break;
}
currentIndex -= 8;
}
if (!match || minRequired42 > 0)
{
continue;
}
matches++;
}
Console.WriteLine("Part 2 ------");
Console.WriteLine("After updating rules 8 and 11, how many messages completely match rule 0?");
Console.WriteLine(matches);
}
