public override string Part2()
{
var testChars = PuzzleInput.ToUpper().Distinct().ToHashSet();
var polymerLength = PuzzleInput.Count();
Parallel.ForEach(testChars, (testChar) =>
{
var shifts = PuzzleInput.ToList();
//Remove 1 problem causing polymer
shifts.RemoveAll(c => c == testChar || c == (char)(testChar + 32));
bool changed;
do
{
changed = false;
for (int i = 0; i < shifts.Count() - 1; i++)
{
if ((shifts[i] - shifts[i + 1]) % 32 == 0 && (shifts[i] != shifts[i + 1]))
{
shifts.RemoveAt(i);
shifts.RemoveAt(i);
changed = true;
}
}
} while (changed);
if (shifts.Count() < polymerLength)
{
lock (varSafe) polymerLength = shifts.Count();
}
});
return(polymerLength.ToString());
}
