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POTicTacToe AI - Minimax Algorithm
 

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  1. POTicTacToe AI - Minimax Algorithm
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    <p>I've just been busy creating an AI for TicTacToe in python. I got the whole thing running the first "round", but when it comes to the second the AI just does nothing, the board just keeps the same. Maybe someone could help me find the errors in my code.</p> <pre><code>import math def drawBoard(): print(board[0] + board[1] + board[2] + "\n" + board[3] + board[4] + board[5] + "\n" + board[6] + board[7] + board[8] + "\n") def getUserMov e(): uin = 0 uin = int(input("Enter your move(" + playerLet + "): ")) while uin &gt; 9 or uin &lt; 1 or board[uin-1] != ' ': print("Invalid Move") uin = int(input("Enter your move (" + playerLet + "): ")) return uin def userMove(): global board move = getUserMove() makeMove(board, move, playerLet) def comMove(): global board val = minimax([board, 0, 0], 8, True) makeMove(board, val[2], comLet) def minimax(node, depth, maximizing): value = getStateValue(node[0], comLet, playerLet) if depth == 0 or math.isinf(value): return [board, value, 0] moves = getPossibleMoves(node[0]) if maximizing: best = [node[0], float("-inf"), 0] for i in moves: boardcopy = [] + node[0] makeMove(boardcopy, i, comLet) val = minimax([boardcopy, value, i], depth - 1, False) if best[1] &lt; val[1]: best = [] + val return best else: best = [node[0], float("inf"), 0] for i in moves: boardcopy = [] + node[0] makeMove(boardcopy, i, playerLet) val = minimax([boardcopy, value, i], depth - 1, True) if best[1] &gt; val[1]: best = [] + val return best def getStateValue(board, maxletter, minletter): val = float(0) if checkWon(board, maxletter): val = float("+inf") if checkWon(board, minletter): val = float("-inf") return val def makeMove(board, move, letter): board[move - 1] = letter def getPossibleMoves(board): pMoves = [] for i in range(0, 8): if board[i] == ' ': pMoves.append(i+1) return pMoves def checkWon(board, letter): if ((board[0] == letter and board[1] == letter and board[2] == letter) or (board[3] == letter and board[4] == letter and board[5] == letter) or (board[6] == letter and board[7] == letter and board[8] == letter) or (board[0] == letter and board[3] == letter and board[6] == letter) or (board[1] == letter and board[4] == letter and board[7] == letter) or (board[2] == letter and board[5] == letter and board[8] == letter) or (board[0] == letter and board[4] == letter and board[8] == letter) or (board[2] == letter and board[4] == letter and board[6] == letter)): return True else: return False board = [' '] * 9 playerLet = 'X' comLet = 'O' won = '' print("--- TicTacToe ---") print("Input like this: \n123\n456\n789") while True: userMove() drawBoard() if checkWon(board, playerLet): won = 'Player' break comMove() drawBoard() if checkWon(board, comLet): won = 'Computer' break print(won + " won!") </code></pre>
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    1. PTQuestion
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    1. UScandraw
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      1. VTUpMod
    1. COI'm still working out how the `minimax` function is supposed to work, but the problem is in that function - `minimax` always returns an illegal move, `0`, which results in the legal move `9` being played every time by the computer.
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      1. POTicTacToe AI - Minimax Algorithm
      1. USBrionius
    2. CO@Brionius I just found out that the illegal move being return is coming from Line 37. If changed to 1 it will always play one. So i checked the code choosing the best move and noticed it didnt work right. I now changed it from `if best[1] > val[1]: best = [] + val` to `if best[1] < val[1]: best[1] = val[1] best[2] = i`
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      1. POTicTacToe AI - Minimax Algorithm
      1. UScandraw
    3. CODid that fix it? Also, is there a reason that you're setting best equal to val plus an empty list, rather than just setting it equal to val?
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      1. POTicTacToe AI - Minimax Algorithm
      1. USseaotternerd
 

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