protected override PartialResult SolveFirst()
{
var(Rules, _, NearbyTickets) = ParseInput(_input);
var result = 0L;
NearbyTickets.SelectMany(l => l.Select(n => n))
.ToList()
.ForEach(n => result += Rules.Values.SelectMany(l => l.Select(r => r))
.All(r => !InRange(n, r)) ? n : 0);
return(new PartialResult(1, result, Stopwatch.Elapsed));
}
protected override PartialResult SolveSecond()
{
var(Rules, MyTicket, NearbyTickets) = ParseInput(_input);
// add my ticket to the nearby tickets
NearbyTickets.Add(MyTicket);
// remove the invalid tickets from collection of nearby's
NearbyTickets.SelectMany(l => l.Select(n => n))
.Where(n => Rules.Values.SelectMany(l => l.Select(r => r)).All(r => !InRange(n, r)))
.ToList()
.ForEach(n => NearbyTickets.RemoveAll(r => r.Contains(n)));
// match each ticket column (number index) with each corresponding rule
// there will be columns that matches several rules
var rules = new Dictionary <string, List <int> >();
foreach (var index in Enumerable.Range(0, Rules.Count()))
{
var column = NearbyTickets.Select(ticket => ticket[index]);
foreach (var rule in Rules)
{
if (column.All(n => rule.Value.Any(r => InRange(n, r))))
{
if (rules.ContainsKey(rule.Key))
{
rules[rule.Key].Add(index);
}
else
{
rules.Add(rule.Key, new List <int> {
index
});
}
}
}
}
// as long as there are rules which can be applied to more than one ticket column,
// eliminate them one by one until there are only rules that applies to one
// ticket column only (hence the use of single - fail fast if something un-
// predicted should occur)
while (rules.Select(r => r.Value).Any(l => l.Count() > 1))
{
foreach (var rule in rules.Where(r => r.Value.Count() == 1))
{
rules.Where(kv => kv.Value.Contains(rule.Value.Single()) && kv.Value.Count() > 1)
.Select(r => r.Key)
.ToList()
.ForEach(key => rules.Where(r => Equals(key, r.Key))
.Select(r => r.Value)
.ToList()
.ForEach(l => l.Remove(rule.Value.Single())));
}
}
// it's time to extract out result - find the rules who begins with the word
// "departure". for each of those corresponding indexes - multiply the ticket
// value for each said index from MyTicket
var result = 1L;
rules.Where(r => r.Key.StartsWith("departure"))
.SelectMany(r => r.Value.Select(n => n))
.ToList()
.ForEach(n => result *= MyTicket[n]);
return(new PartialResult(2, result, Stopwatch.Elapsed));
}