GoLadderStatus GoLadderUtil::LadderStatus(const GoBoard& bd, SgPoint prey,
bool twoLibIsEscape,
SgPoint* toCapture,
SgPoint* toEscape)
{
SG_ASSERT(bd.IsValidPoint(prey));
SG_ASSERT(bd.Occupied(prey));
#ifndef NDEBUG
SgHashCode oldHash = bd.GetHashCode();
#endif
// Unsettled only if can capture when hunter plays first, and can escape
// if prey plays first.
GoLadder ladder;
SgBlackWhite preyColor = bd.GetStone(prey);
SgVector<SgPoint> captureSequence;
GoLadderStatus status = GO_LADDER_ESCAPED;
if (ladder.Ladder(bd, prey, SgOppBW(preyColor), &captureSequence,
twoLibIsEscape) < 0)
{
SgVector<SgPoint> escapeSequence;
if (ladder.Ladder(bd, prey, preyColor, &escapeSequence,
twoLibIsEscape) < 0)
status = GO_LADDER_CAPTURED;
else
{
status = GO_LADDER_UNSETTLED;
// Unsettled = ladder depends on who plays first, so there must
// be a move that can be played.
SG_ASSERT(captureSequence.NonEmpty());
// escapeSequence can be empty in 2 libs, prey to play case
SG_ASSERT(twoLibIsEscape || escapeSequence.NonEmpty());
if (toCapture)
*toCapture = captureSequence.Front();
if (toEscape)
*toEscape = escapeSequence.IsEmpty() ? SG_PASS :
escapeSequence.Front();
}
}
#ifndef NDEBUG
// Make sure Ladder didn't change the board position.
SG_ASSERT(oldHash == bd.GetHashCode());
#endif
return status;
}
SgPoint GoLadderUtil::TryLadder(const GoBoard& bd, SgPoint prey,
SgBlackWhite firstPlayer)
{
SgVector<SgPoint> sequence;
bool isCaptured = Ladder(bd, prey, firstPlayer, true, &sequence);
// if move is same color as prey, we want to escape
// else we want to capture.
SgPoint p;
if (isCaptured != (firstPlayer == bd.GetStone(prey)))
p = sequence.IsEmpty() ? SG_PASS : sequence.Front();
else
p = SG_NULLMOVE;
return p;
}
