minimaxAISequential.py

import sys
import time
import minimaxCommon as mmUtil

activePlayer = -1
opponentPlayer = -1
maxTime = 20
startTime = 0
maxDepth = 7

# returns an action
def alpha_beta_search(board):
    print "[INFO] SEQUENTIAL"
    global startTime
    startTime = time.clock()
    v = max_value_first(board, float('-inf'), float('inf'), 0)
    return v[1]

# returns a utility value
def max_value_first(board, alpha, beta, depth):
    v = float('-inf')
    move = 3
    for a in mmUtil.get_moves(board):
        vMin = min_value(mmUtil.make_move(board,a,activePlayer), alpha, beta, depth+1)
        if v >= vMin:
            move = move
        else:
            v = vMin
            move = a
        if v >= beta:
            return (v, move)
        alpha = max(alpha,v)
    return (v, move)

# returns a utility value
def max_value(board, alpha, beta, depth):
    if mmUtil.terminal_test(board, opponentPlayer, depth, startTime, maxTime, maxDepth):
        return mmUtil.utility(board, activePlayer)
    v = float('-inf')
    for a in mmUtil.get_moves(board):
        v = max(v, min_value(mmUtil.make_move(board,a,activePlayer), alpha, beta, depth+1))
        if v >= beta:
            return v
        alpha = max(alpha,v)
    return v

def min_value(board, alpha, beta, depth):
    if mmUtil.terminal_test(board, activePlayer, depth, startTime, maxTime, maxDepth):
        return mmUtil.utility(board, activePlayer)
    v = float('inf')
    for a in mmUtil.get_moves(board):
        v = min(v, max_value(mmUtil.make_move(board,a,opponentPlayer), alpha, beta, depth+1))
        if v <= alpha:
            return v
        beta = min(beta, v)
    return v

def run_AI(board, ID):
    global activePlayer
    global opponentPlayer
    activePlayer = ID
    if activePlayer == 0:
        opponentPlayer = 1
    else:
        opponentPlayer = 0
    v = alpha_beta_search(board)
    return str(v)