public UctNode UCTSelect(UctNode UctNode)
{
UctNode res = null;
UctNode next = UctNode.Child;
double best_uct = 0;
while (next != null)
{ // for all children
double uctvalue;
if (next.Visits > 0)
{
double winrate = next.GetWinRate();
double uct = UCTK * Math.Sqrt(Math.Log(UctNode.Visits) / next.Visits);
uctvalue = winrate + uct;
}
else
{
// Always play a random unexplored move first
uctvalue = 10000 + 1000 * _random.NextDouble();
}
if (uctvalue > best_uct)
{ // get max uctvalue of all children
best_uct = uctvalue;
res = next;
}
next = next.Sibling;
}
return res;
}
public UctNode GetBestChild(UctNode root)
{
UctNode Child = root.Child;
UctNode best_child = null;
int best_visits = -1;
while (Child != null)
{ // for all children
if (Child.Visits > best_visits)
{
best_child = Child;
best_visits = Child.Visits;
}
Child = Child.Sibling;
}
return best_child;
}
// return 0=lose 1=win for current player to move
private int PlaySimulation(Field field, UctNode n)
{
int randomresult = 0;
if (n.Child == null && n.Visits < 10)
{ // 10 simulations until chilren are expanded (saves memory)
randomresult = PlayRandomGame(field);
}
else
{
if (n.Child == null)
CreateChildren(field, n);
UctNode next = UCTSelect(n); // select a move
if (next == null) { /* ERROR */ }
field.MakeMove(next.Pos);
int res = PlaySimulation(field, next);
randomresult = 1 - res;
}
n.Update(1 - randomresult); //update UctNode (UctNode-wins are associated with moves in the Nodes)
return randomresult;
}
// generate a move, using the uct algorithm
private int UCTSearch(int numsim)
{
root = new UctNode(0); //init uct tree
CreateChildren(Field, root);
Field clone;
for (int i = 0; i < numsim; i++)
{
clone = Field.Clone();
PlaySimulation(clone, root);
}
UctNode n = GetBestChild(root);
return n.Pos;
}
// expand children in UctNode
private void CreateChildren(Field field, UctNode parent)
{
UctNode last = parent;
for (int i = 1; i <= field.Width; i++)
for (int j = 1; j <= field.Height; j++)
{
var pos = Field.GetPosition(i, j);
if (field[pos].IsPuttingAllowed())
{
UctNode UctNode = new UctNode(pos);
if (last == parent)
last.Child = UctNode;
else
last.Sibling = UctNode;
last = UctNode;
}
}
}