/// <summary>
/// Returns the table with updated stability values after given move.
/// </summary>
/// <param name="table">Table after the move with original stability state.</param>
/// <returns>The table after given move with updated stability values.</returns>
public static ReversiTable GetTableWithUpdatedStability(this ReversiTable table)
{
// Start with all currently unstable cells.
Queue <Position> unstableCells = new Queue <Position>(table.GetUnstableCells().ToList());
// Process all unstable cells.
while (unstableCells.Count > 0)
{
Position candidate = unstableCells.Dequeue();
if (!table.GetStable(candidate.Item1, candidate.Item2) &&
table.IsStable(candidate))
{
// Mark the cell as stable.
table.SetStable(true, candidate.Item1, candidate.Item2);
// All unstable neighbors need to be checked again.
foreach (Position delta in ReversiConstants.Directions)
{
Position neighbor = new Position(candidate.Item1 + delta.Item1, candidate.Item2 + delta.Item2);
if (neighbor.Item1 >= 0 && neighbor.Item1 < ReversiTable.Size &&
neighbor.Item2 >= 0 && neighbor.Item2 < ReversiTable.Size &&
table.GetValue(neighbor.Item1, neighbor.Item2) != Value.None &&
!table.GetStable(neighbor.Item1, neighbor.Item2))
{
unstableCells.Enqueue(neighbor);
}
}
}
}
return(table);
}
/// <summary>
/// Returns the table after given move.
/// </summary>
/// <param name="move">The move.</param>
/// <returns>The table after given move.</returns>
private ReversiTable GetTableForMove(Tuple <Position, IEnumerable <Position> > move)
{
Position cell = move.Item1;
ReversiTable tableAfterMove = stateTable;
tableAfterMove.SetValue(Player, cell.Item1, cell.Item2);
foreach (Position direction in move.Item2)
{
int dx = cell.Item1 + direction.Item1;
int dy = cell.Item2 + direction.Item2;
while (
dx >= 0 && dx < ReversiTable.Size &&
dy >= 0 && dy < ReversiTable.Size &&
stateTable.GetValue(dx, dy) == Opponent)
{
tableAfterMove.SetValue(Player, dx, dy);
dx += direction.Item1;
dy += direction.Item2;
}
}
return(tableAfterMove);
}
/// <summary>
/// Gets the list of currently unstable occupied cells that are potentially stable.
/// </summary>
/// <param name="table">The table.</param>
/// <returns>The list of unstable cells.</returns>
public static IEnumerable <Position> GetUnstableCells(this ReversiTable table)
{
for (int i = 0; i < ReversiTable.Size; ++i)
{
for (int j = 0; j < ReversiTable.Size; ++j)
{
if (table.GetValue(i, j) != Value.None && !table.GetStable(i, j))
{
yield return(new Position(i, j));
}
}
}
}
/// <summary>
/// Gets the stability score.
/// </summary>
/// <param name="table">The table.</param>
/// <returns>The difference between maximizing and minimizing players' stable cells.</returns>
public static int GetStabilityScore(this ReversiTable table)
{
int score = 0;
for (int i = 0; i < ReversiTable.Size; ++i)
{
for (int j = 0; j < ReversiTable.Size; ++j)
{
if (table.GetStable(i, j))
{
score += table.GetValue(i, j) == Value.Maximizing ? 1 : -1;
}
}
}
return(score);
}
/// <summary>
/// Initializes a new instance of the <see cref="ReversiNode" /> class.
/// </summary>
/// <param name="table">The game state.</param>
/// <param name="currentPlayer">Current player.</param>
/// <param name="playerCanPass">Indicates whether the current player can pass a move.</param>
private ReversiNode(
ReversiTable table,
Value currentPlayer,
bool playerCanPass = true)
{
canPass = playerCanPass;
stateTable = table;
heuristics = new Lazy <int>(
() => GetHeuristics(),
LazyThreadSafetyMode.ExecutionAndPublication);
children = new Lazy <IReadOnlyList <ReversiNode> >(
() => GetChildren(),
LazyThreadSafetyMode.ExecutionAndPublication);
Debug.Assert(currentPlayer != Value.None, "Verifying that the player value is valid.");
Player = currentPlayer;
Opponent = currentPlayer == Value.Maximizing
? Value.Minimizing
: Value.Maximizing;
}
/// <summary>
/// Initializes a new instance of the <see cref="ReversiNode" /> class.
/// </summary>
/// <param name="table">The game state.</param>
/// <param name="currentPlayer">Current player.</param>
/// <param name="playerCanPass">Indicates whether the current player can pass a move.</param>
private ReversiNode(
ReversiTable table,
Value currentPlayer,
bool playerCanPass = true)
{
canPass = playerCanPass;
stateTable = table;
heuristics = new Lazy<int>(
() => GetHeuristics(),
LazyThreadSafetyMode.ExecutionAndPublication);
children = new Lazy<IReadOnlyList<ReversiNode>>(
() => GetChildren(),
LazyThreadSafetyMode.ExecutionAndPublication);
Debug.Assert(currentPlayer != Value.None, "Verifying that the player value is valid.");
Player = currentPlayer;
Opponent = currentPlayer == Value.Maximizing
? Value.Minimizing
: Value.Maximizing;
}
/// <summary>
/// Computes all children nodes of current node.
/// </summary>
/// <returns>Children nodes.</returns>
private IReadOnlyList <ReversiNode> GetChildren()
{
var children = GetValidMoves(Player).Select(move =>
{
ReversiTable table = GetTableForMove(move);
ReversiTable stabilityTable = table.GetTableWithUpdatedStability();
return(new ReversiNode(stabilityTable, Opponent));
}).ToList();
// Check whether it is a terminal node or whether the current player passes.
if (children.Count == 0 && canPass)
{
ReversiNode nextNode = new ReversiNode(stateTable, Opponent, false);
if (nextNode.Children.Count > 0)
{
children.Add(nextNode);
}
}
return(children.AsReadOnly());
}
/// <summary>
/// Initializes a new instance of the <see cref="ReversiNode" /> class with the starting position.
/// </summary>
public ReversiNode() : this(
ReversiTable.InitialState(),
Value.Maximizing)
{
}
/// <summary>
/// Determines whether the specified cell is stable.
/// </summary>
/// <param name="table">The table.</param>
/// <param name="cell">The cell.</param>
/// <returns>True if the cell is stable, false otherwise.</returns>
public static bool IsStable(this ReversiTable table, Position cell)
{
if (table.GetValue(cell.Item1, cell.Item2) == Value.None)
{
return(false);
}
foreach (Position delta in ReversiConstants.StabilityDirections)
{
Value player = table.GetValue(cell.Item1, cell.Item2);
Position positive = new Position(cell.Item1 + delta.Item1, cell.Item2 + delta.Item2);
Position negative = new Position(cell.Item1 - delta.Item1, cell.Item2 - delta.Item2);
// If one of the cell is on the edge, the direction is stable.
if (positive.Item1 < 0 || positive.Item1 >= ReversiTable.Size ||
positive.Item2 < 0 || positive.Item2 >= ReversiTable.Size ||
negative.Item1 < 0 || negative.Item1 >= ReversiTable.Size ||
negative.Item2 < 0 || negative.Item2 >= ReversiTable.Size)
{
continue;
}
// If at least one of the neighbors is a stable cell belonging to the same player,
// the direction is stable.
if ((table.GetStable(positive.Item1, positive.Item2) &&
table.GetValue(positive.Item1, positive.Item2) == player) ||
(table.GetStable(negative.Item1, negative.Item2) &&
table.GetValue(negative.Item1, negative.Item2) == player))
{
continue;
}
// If all cells in the line of direction are filled, the direction is stable.
do
{
if (table.GetValue(positive.Item1, positive.Item2) == Value.None)
{
return(false);
}
positive = new Position(positive.Item1 + delta.Item1, positive.Item2 + delta.Item2);
}while (positive.Item1 >= 0 && positive.Item1 < ReversiTable.Size &&
positive.Item2 >= 0 && positive.Item2 < ReversiTable.Size);
do
{
if (table.GetValue(negative.Item1, negative.Item2) == Value.None)
{
return(false);
}
negative = new Position(negative.Item1 - delta.Item1, negative.Item2 - delta.Item2);
}while (negative.Item1 >= 0 && negative.Item1 < ReversiTable.Size &&
negative.Item2 >= 0 && negative.Item2 < ReversiTable.Size);
// The line is filled.
continue;
}
// No unstable directions found.
return(true);
}