public void Notify(int index, Quadstate before, Quadstate after)
{
var a = after == Quadstate.Yes || after == Quadstate.Contradiction;
var b = before == Quadstate.Yes || before == Quadstate.Contradiction;
if (a && !b)
{
VisitNearby(index, false);
}
if (b && !a)
{
// Must be backtracking.
// The main backtrack mechanism will handle undoing bans, and
// undos are always in order, so we just need to reverse VisitNearby
VisitNearby(index, true);
}
}
public void Notify(int index, Quadstate before, Quadstate after)
{
switch (before)
{
case Quadstate.No: NoCount--; break;
case Quadstate.Maybe: MaybeCount--; break;
case Quadstate.Yes: YesCount--; break;
}
switch (after)
{
case Quadstate.No: NoCount++; break;
case Quadstate.Maybe: MaybeCount++; break;
case Quadstate.Yes: YesCount++; break;
}
}
public static bool Possible(this Quadstate v) => (int)v >= 0;
public static bool IsContradiction(this Quadstate v) => v == Quadstate.Contradiction;
public static bool IsNo(this Quadstate v) => v == Quadstate.No;
public static bool IsMaybe(this Quadstate v) => v == Quadstate.Maybe;
public static bool IsYes(this Quadstate v) => v == Quadstate.Yes;
public bool Next(int index, Quadstate selected)
{
switch (state)
{
case State.Initial:
if (selected.IsYes())
{
state = State.InRun;
runCount = 1;
runStartIndex = index;
}
return(false);
case State.JustAfterRun:
if (selected.IsYes())
{
state = State.InRun;
runCount = 1;
runStartIndex = index;
goto checkCases;
}
else
{
state = State.Initial;
prevRunCount = 0;
runCount = 0;
}
return(false);
case State.InRun:
if (selected.IsYes())
{
state = State.InRun;
runCount += 1;
if (runCount > max)
{
// Immediate contradiction
return(true);
}
goto checkCases;
}
else
{
// Also case 1.
if (runCount == max)
{
if (selected.Possible())
{
banAt(index);
}
}
state = State.JustAfterRun;
prevRunCount = runCount;
runCount = 0;
}
return(false);
}
// Unreachable
throw new Exception("Unreachable");
checkCases:
// Have we entered case 1 or 2?
if (prevRunCount + runCount == max)
{
// Ban on the previous end of the run
if (runStartIndex == 0)
{
if (periodic)
{
banAt(indexCount - 1);
}
}
else
{
banAt(runStartIndex - 1);
}
}
return(false);
}