bool GoEyeUtil::CheckInterior(const GoBoard& bd, const SgPointSet& area,
SgBlackWhite opp, bool checkBlocks)
{
bool hasSingleNbPoint = false;
int nuPoints = 0;
for (SgSetIterator it(area); it; ++it)
{
const SgPoint p(*it);
if (bd.IsEmpty(p))
{
int nuNbs = 0;
if (area.Contains(p + SG_NS))
++nuNbs;
if (area.Contains(p - SG_NS))
++nuNbs;
if (area.Contains(p + SG_WE))
++nuNbs;
if (area.Contains(p - SG_WE))
++nuNbs;
if (nuNbs == 1)
hasSingleNbPoint = true;
else if (nuNbs > 2)
return false;
}
else if (p == bd.Anchor(p))
{
if (bd.GetColor(p) != opp)
// if own stones on inside: not a tree shape.
return false;
int nuLibs = bd.NumLiberties(p);
if (nuLibs == 1)
hasSingleNbPoint = true;
else if (checkBlocks && nuLibs > 2)
return false;
}
++nuPoints;
}
return nuPoints == 1 || hasSingleNbPoint;
}
void GoLadderUtil::FindLadderEscapeMoves(const GoBoard& bd, SgPoint prey,
SgVector<SgPoint>& escapeMoves)
{
SG_ASSERT(bd.NumLiberties(prey) == 1);
SG_ASSERT(escapeMoves.IsEmpty());
SgPoint p = bd.TheLiberty(prey);
SgVector<SgPoint> candidates;
candidates.PushBack(p);
if (IsLadderEscapeMove(bd, prey, p))
escapeMoves.PushBack(p);
for (GoAdjBlockIterator<GoBoard> it(bd, prey, 1); it; ++it)
{
// check if prey can escape by capturing *it on p.
SgPoint p = bd.TheLiberty(*it);
if (! candidates.Contains(p))
{
candidates.PushBack(p);
if (IsLadderEscapeMove(bd, prey, p))
escapeMoves.PushBack(p);
}
}
}
bool GoLadderUtil::IsLadderEscapeMove(const GoBoard& constBd,
SgPoint prey, SgPoint firstMove)
{
SG_ASSERT(constBd.NumLiberties(prey) == 1);
GoModBoard mbd(constBd);
GoBoard& bd = mbd.Board();
const SgBlackWhite defender = bd.GetStone(prey);
const SgBlackWhite attacker = SgOppBW(defender);
GoRestoreToPlay r(bd);
bd.SetToPlay(defender);
if (PlayIfLegal(bd, firstMove, defender))
{
GoLadder ladder;
bool isCapture = ladder.Ladder(bd, prey, attacker,
0, false/*twoLibIsEscape*/
) < 0;
bd.Undo();
return ! isCapture;
}
else
return false;
}
bool GoEyeUtil::NumberOfMoveToEye2(const GoBoard& board, SgBlackWhite color,
SgPoint p, int& nummoves)
{
nummoves = 0;
bool capturing = false;
SgVector<SgPoint> usedpoints;
usedpoints.PushBack(p);
SgPointSet counted;
// Can never turn own stone into an eye
if (board.IsColor(p, color))
return false;
// If opponent stone then it must be captured to make eye
if (board.IsColor(p, SgOppBW(color)))
{
capturing = true;
// If it is obviously safe then it can never be an eye
if (SinglePointSafe2(board, p)) // Quick, naive safety test
return false;
for (GoBoard::LibertyIterator libit(board, p); libit; ++libit)
counted.Include(*libit);
}
// Count immediate adjacencies
for (SgNb4Iterator nb(p); nb; ++nb)
{
SgPoint adj = *nb;
// Empty points must be filled
if (board.IsColor(adj, SG_EMPTY))
{
counted.Include(adj);
}
// If adjacent opponent then can never be an eye
else if (board.IsColor(adj, SgOppBW(color)))
{
if (capturing)
counted.Include(adj); // must capture and then fill
else
return false;
}
}
// Up to one diagonal can be ignored: estimate most costly
SgPoint toignore = SG_NULLPOINT;
int maxcost = 0;
int infcost = 1000;
if (board.Line(p) > 1)
{
for (SgNb4DiagIterator nbd(p); nbd; ++nbd)
{
SgPoint diag = *nbd;
int cost = 0;
if ( board.IsColor(diag, SG_EMPTY)
&& ! IsSinglePointEye2(board, diag, color, usedpoints))
{
cost = 1;
}
else if (board.IsColor(diag, SgOppBW(color)))
{
// quick safety test
if (SinglePointSafe2(board, diag))
cost = infcost;
else
cost = board.NumLiberties(diag);
}
if (cost > maxcost)
{
maxcost = cost;
toignore = diag;
}
}
}
// Now mark points that must be played to secure diagonals
for (SgNb4DiagIterator nbd(p); nbd; ++nbd)
{
SgPoint diag = *nbd;
if (diag == toignore)
continue;
// Empty points must be filled (unless they are eyes)
if ( board.IsColor(diag, SG_EMPTY)
&& ! IsSinglePointEye2(board, diag, color, usedpoints))
{
counted.Include(diag);
}
// Opponent stones on diagonals must be captured and filled
else if (board.IsColor(diag, SgOppBW(color)))
{
if (SinglePointSafe2(board, diag))
return false;
else
{
counted.Include(diag);
for (GoBoard::LibertyIterator libit(board, diag); libit;
++libit)
counted.Include(*libit);
}
}
}
nummoves = counted.Size();
return true;
}
