public static int Part2(string input = null)
{
input ??= Input.ReadAllText(nameof(Day19));
var inputParts = input.Split("\n\n",
StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
var ruleStrings = inputParts[0].Split("\n");
var messages = inputParts[1]
.Split("\n", StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries);
var rules = CreateRules(ruleStrings);
rules[11] = Rule.Parse("11: 42 31 | 42 11 31");
rules[8] = Rule.Parse("8: 42 | 42 8");
var valid = 0;
foreach (var message in messages)
{
if (GenerateVariants(0, rules, message).Contains(message))
{
valid++;
}
}
return(valid);
}
public static Dictionary <int, Rule> CreateRules(string[] ruleStrings)
{
var rules = new Dictionary <int, Rule>();
foreach (var ruleString in ruleStrings)
{
var rule = Rule.Parse(ruleString);
rules.Add(rule.Id, rule);
}
return(rules);
}
public int ComputePart1(IEnumerable <string> input = null)
{
input = input ?? LoadRawData();
var parts = string.Join("\n", input).Split("\n\n");
var rules = parts[0].Split("\n").Select(x => Rule.Parse(x));
var otherTickets = parts[2].Split("\n")
.Skip(1)
.Select(x => Ticket.Parse(x))
.ToArray();
var invalidValues = otherTickets
.SelectMany(ticket => ticket.GetInvalidValues(rules));
return(invalidValues.Sum());
}
public long ComputePart2(IEnumerable <string> input = null)
{
input = input ?? LoadRawData();
var parts = string.Join("\n", input).Split("\n\n");
var rules = parts[0].Split("\n").Select(x => Rule.Parse(x)).ToArray();
var myTicket = Ticket.Parse(parts[1].Split("\n")[1]);
var otherTickets = parts[2].Split("\n")
.Skip(1)
.Select(x => Ticket.Parse(x))
.ToArray();
var validTickets = otherTickets
.Where(x => x.GetIsValid(rules))
.ToArray();
var ticketWidth = validTickets[0].Fields.Count();
var allPositions = (1 << ticketWidth) - 1;
var powersOfTwo = Enumerable.Range(0, ticketWidth)
.Select(x => 1 << x)
.ToHashSet();
var ruleOptions = Enumerable
.Repeat(allPositions, ticketWidth)
.ToArray();
var found = 0;
foreach (var ticket in validTickets)
{
foreach (var(rule, ruleNo) in rules.Select((r, idx) => (r, idx)))
{
var opts = ruleOptions[ruleNo];
if (!powersOfTwo.Contains(opts))
{
opts = opts & ticket.MapRule(rule);
}
ruleOptions[ruleNo] = opts;
if (powersOfTwo.Contains(opts))
{
found = found | opts;
}
}
found = ReduceOptions(ruleOptions, found, powersOfTwo);
}
ReduceOptions(ruleOptions, found, powersOfTwo);
if (ruleOptions.Except(powersOfTwo).Any())
{
throw new System.Exception("didn't filter them all!");
}
var ruleIndexes = ruleOptions
.Select(x => (int)System.Math.Log2(x))
.ToArray();
var rulesInOrder = ruleIndexes
.Zip(rules, (idx, rule) => new { idx, rule })
.OrderBy(x => x.idx)
.ToArray();
foreach (var(ticket, ticketIdx) in validTickets.Select((x, idx) => (x, idx)))
{
foreach (var(rule, val) in rulesInOrder.Zip(ticket.Fields, (r, v) => (r, v)))
{
if (!rule.rule.Contains(val))
{
throw new System.Exception($"rule {rule.rule.Name} at position {rule.idx} does not match value {val} on ticket {ticketIdx + 1}");
}
}
}
var departureRuleIndexes = rulesInOrder
.Where(x => x.rule.Name.StartsWith("departure"))
.Select(x => x.idx)
.ToArray();
var departureValues = myTicket.Fields
.Select((val, idx) => new { val, idx })
.Where(x => departureRuleIndexes.Contains(x.idx))
.Select(x => x.val)
.ToArray();
return(departureValues.Aggregate(1L, (p, v) => p * v));
}
