private static long ProcessPacket(BinaryString b, List <long> versions)
{
long version = b.ReadBits(3);
long type = b.ReadBits(3);
versions.Add(version);
if (type == 4)
{
// Base case. Literals contain no sub packets, so just calculate the value they represent and return
return(ProcessLiteral(b));
}
List <long> subResults = new();
// Operator case. Determine how to read the sub packets
long lengthTypeId = b.ReadBits(1);
if (lengthTypeId == 0)
{
// Sub packet section is defined by the number of bits
long subPacketBitLength = b.ReadBits(15);
long positionBefore = b.Position;
long goalPosition = positionBefore + subPacketBitLength;
while (b.Position < goalPosition)
{
long subResult = ProcessPacket(b, versions);
subResults.Add(subResult);
}
}
else if (lengthTypeId == 1)
{
// Sub packet section is defined by the number of packets
long numberOfSubPackets = b.ReadBits(11);
for (int i = 0; i < numberOfSubPackets; i++)
{
long subResult = ProcessPacket(b, versions);
subResults.Add(subResult);
}
}
// Evaluate the different operators against the sub packet results
return(type switch
{
0 => subResults.Sum(),
1 => subResults.Aggregate(1L, (acc, x) => acc * x),
2 => subResults.Min(),
3 => subResults.Max(),
5 => subResults[0] > subResults[1] ? 1 : 0,
6 => subResults[0] < subResults[1] ? 1 : 0,
7 => subResults[0] == subResults[1] ? 1 : 0,
_ => throw new NotSupportedException(type.ToString()),
});