Golang Board.AllLegalMoves方法代码示例

// Roughly orders moves in order of most likely to be good to least.
// Examines all checks first, followed by captures, followed by good moves.
// "Good moves" are sorted by their board evaluation after they are played.
// If quiescence is set to true, then only checks and captures are returned.
func orderedMoves(b *engine.Board, quiescence bool) []*engine.Move {
	checks := make([]*engine.Move, 0)
	captures := make([]*engine.Move, 0)
	rest := make([]*engine.Move, 0)
	// parentscore := EvalBoard(b)
	for _, move := range b.AllLegalMoves() {
		b.ForceMove(move)
		if b.IsCheck(b.Turn) {
			checks = append(checks, move)
		} else if move.Capture != 0 {
			captures = append(captures, move)
		} else if !quiescence {
			childscore := EvalBoard(b) * float64(b.Turn*-1)
			// if (b.Turn == -1 && childscore > parentscore) || (b.Turn == 1 && childscore < parentscore) {
			move.Score = childscore
			rest = append(rest, move)
			// }
		}
		b.UndoMove(move)
	}
	if !quiescence {
		sort.Sort(sort.Reverse(ByScore(rest)))
	}
	orderedmoves := make([]*engine.Move, len(checks)+len(captures)+len(rest))
	index := 0
	for _, l := range [][]*engine.Move{checks, captures, rest} {
		for _, m := range l {
			m.Score = 0
			orderedmoves[index] = m
			index++
		}
	}
	return orderedmoves
}

// First-level NegaScout search function.
// When called, alpha and beta should be set to the lowest and highest values possible.
func NegaScout(b *engine.Board, depth int, alpha, beta float64) *engine.Move {
	if b.IsOver() != 0 || depth == 0 {
		b.Lastmove.Score = EvalBoard(b)
		return &b.Lastmove
	}
	var move engine.Move

	// not indended for actual use
	orderedmoves := b.AllLegalMoves()

	var score float64
	for i, m := range orderedmoves {
		childboard := b.CopyBoard()
		childboard.Move(m)
		if i != 0 {
			score = -NegaScoutChild(childboard, depth-1, -alpha-1, -alpha)
			if alpha < score && score < beta {
				score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
			}
		} else {
			score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
		}
		alpha = math.Max(alpha, score)
		if alpha >= beta {
			move = *m.CopyMove()
			move.Score = alpha
			break
		}
	}
	return &move
}

// Child level NegaScout search function.
// Unlike its parent, only returns score and not full move
func NegaScoutChild(b *engine.Board, depth int, alpha, beta float64) float64 {
	if b.IsOver() != 0 || depth == 0 {
		return EvalBoard(b)
	}

	// not indended for actual use
	orderedmoves := b.AllLegalMoves()

	var score float64
	for i, m := range orderedmoves {
		childboard := b.CopyBoard()
		childboard.Move(m)
		if i != 0 {
			score = -NegaScoutChild(childboard, depth-1, -alpha-1, -alpha)
			if alpha < score && score < beta {
				score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
			}
		} else {
			score = -NegaScoutChild(childboard, depth-1, -beta, -alpha)
		}
		alpha = math.Max(alpha, score)
		if alpha >= beta {
			break
		}
	}
	return alpha
}

// First-level negamax search function.
func NegaMax(b *engine.Board, depth int) *engine.Move {
	if b.IsOver() != 0 || depth == 0 {
		b.Lastmove.Score = EvalBoard(b)
		return &b.Lastmove
	}
	var move engine.Move
	move.Score = LOSS
	for _, m := range b.AllLegalMoves() {
		childboard := b.CopyBoard()
		childboard.Move(m)
		childscore := -NegaMaxChild(childboard, depth-1)
		if childscore > move.Score {
			move = *m.CopyMove()
			move.Score = childscore
			if move.Score == WIN {
				return &move
			}
		}
	}
	return &move
}

// Standard minmax search with alpha beta pruning.
// Initial call: alpha set to lowest value, beta set to highest.
// Top level returns a move.
func AlphaBeta(b *engine.Board, depth int, alpha, beta float64) *engine.Move {
	if b.IsOver() != 0 || depth == 0 {
		return nil
	}
	var bestmove *engine.Move = nil
	var result float64
	movelist := orderedMoves(b, false)
	if b.Turn == 1 {
		for _, move := range movelist {
			b.ForceMove(move)
			if move.Capture != 0 || b.IsCheck(b.Turn) {
				result = AlphaBetaChild(b, depth-1, alpha, beta, true)
			} else {
				result = AlphaBetaChild(b, depth-1, alpha, beta, false)
			}
			b.UndoMove(move)
			if result > alpha {
				alpha = result
				bestmove = move
				bestmove.Score = alpha
			}
			if alpha >= beta {
				bestmove = move
				bestmove.Score = alpha
				return bestmove
			}
		}
		if bestmove == nil {
			return b.AllLegalMoves()[0]
		}
		return bestmove
	} else {
		for _, move := range movelist {
			b.ForceMove(move)
			if move.Capture != 0 || b.IsCheck(b.Turn) {
				result = AlphaBetaChild(b, depth-1, alpha, beta, true)
			} else {
				result = AlphaBetaChild(b, depth-1, alpha, beta, false)
			}
			if LOG {
				fmt.Println(move.ToString(), result)
			}
			b.UndoMove(move)
			if result < beta {
				beta = result
				bestmove = move
				bestmove.Score = beta
			}
			if beta <= alpha {
				bestmove = move
				bestmove.Score = beta
				return bestmove
			}
		}
		if bestmove == nil {
			return b.AllLegalMoves()[0]
		}
		return bestmove
	}
	if bestmove == nil {
		return b.AllLegalMoves()[0]
	}
	return bestmove
}