PyChessGame/computer.py at main · ElDEEB21/PyChessGame · GitHub

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import random

pieceScore = {"K": 0, "Q": 9, "R": 5, "B": 3, "N": 3, "p": 1}
CHECKMATE = 1000
STALEMATE = 0
DEPTH = 0

def findRandomMove(validMoves):
    return random.choice(validMoves)

def findBestMoveAlphaBeta(gs, validMoves, AIDepth=0):
    global nextMove
    global DEPTH
    DEPTH= AIDepth
    nextMove = None
    random.shuffle(validMoves)
    alphaBeta(gs, validMoves, AIDepth, -CHECKMATE, CHECKMATE, 1 if gs.whiteToMove else -1)
    return nextMove

def alphaBeta(gs, validMoves, depth, alpha, beta, turnMultiplier):
    global nextMove
    global DEPTH
    if depth == 0:
        return scoreBoard(gs)
    if turnMultiplier == 1:
        maxScore = -CHECKMATE
        for move in validMoves:
            gs.makeMove(move)
            nextMoves = gs.getValidMoves()
            score = alphaBeta(gs, nextMoves, depth - 1, alpha, beta, -turnMultiplier)
            if score > maxScore:
                maxScore = score
                if depth == DEPTH:
                    nextMove = move
            gs.undoMove()
            alpha = max(alpha, maxScore)
            if alpha >= beta:
                break
        return maxScore
    else:
        minScore = CHECKMATE
        for move in validMoves:
            gs.makeMove(move)
            nextMoves = gs.getValidMoves()
            score = alphaBeta(gs, nextMoves, depth - 1, alpha, beta, -turnMultiplier)
            if score < minScore:
                minScore = score
                if depth == DEPTH:
                    nextMove = move
            gs.undoMove()
            beta = min(beta, minScore)
            if alpha >= beta:
                break
        return minScore

def scoreBoard(gs):
    if gs.checkmate:
        if gs.whiteToMove:
            return -CHECKMATE
        else:
            return CHECKMATE
    elif gs.stalemate:
        return STALEMATE
    score = scoreMaterial(gs.board)
    return score

# Score the board based on material
def scoreMaterial(board):
    score = 0
    for row in board:
        for square in row:
            if square[0] == 'w':
                score += pieceScore[square[1]]
            elif square[0] == 'b':
                score -= pieceScore[square[1]]
    return score