My Little Scripts - tic-tac-toe.html - PHP ASP Scripts, JavaScript, HTML

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TIC-TAC-TOE.HTML
Found out that ai_play() should should not have had of a double loop. Fixed next_available_square(). Unlike the previous versions, this one is the result of many days of meticulous debugging. I still have not succeeded in creating a game that cannot be defeated. The flaw in this particular version is that it tries to avoid defeat, but neglects the weight of possible future wins and ties.
see also : wheel-of-fortune.php, tic-tac-toe.html
<html>
<head>
<title>tic tac toe</title>

<script>
function create_tic_tac_toe_ai_array()
         {
         ai_array = new Array(9);

         for(var index = 0; index < ai_array.length; index++)
            {
            ai_array[index] = new Array(ai_array.length - index);
            for(var index2 = 0; index2 < ai_array[index].length; index2++)
                ai_array[index][index2] = index2;
            }

         return(ai_array);
         }

function randomise_ai_array(tic_tac_toe_ai_array)
         {
         for(var index = 0; index < tic_tac_toe_ai_array.length; index++)
            for(var index2 = 0; index2 < tic_tac_toe_ai_array[index].length; index2++)
               {
               temp = tic_tac_toe_ai_array[index][index2];
               rand = parseInt(Math.random() * tic_tac_toe_ai_array[index].length);
               tic_tac_toe_ai_array[index][index2] = tic_tac_toe_ai_array[index][rand];
               tic_tac_toe_ai_array[index][rand] = temp;
               }
         }

function create_tic_tac_toe()
         {
         this.Letter = '';
         this.Play = -1;
         }

function create_tic_tac_toe_array()
         {
         game_array = new Array(9);

         for(var index = 0; index < ai_array.length; index++)
             game_array[index] = new create_tic_tac_toe();

         return(game_array);
         }

function next_available_square(tic_tac_toe_array, square)
         {
         empty_squares = 0;

         for(var index = 0; empty_squares <= square; index++)
            {
            if(tic_tac_toe_array[index].Letter == '')
              {
              empty_squares++;
              }
            }

         return(index - 1);
         }

function ai_play(tic_tac_toe_array, tic_tac_toe_ai_array, turn_number, trial_number)
         {
         var index = turn_number + trial_number;

         var possible_player_wins = 0;

         var possible_outcomes = new Array(tic_tac_toe_ai_array[index].length);

         //Each increment in this loop is a possible move.
         for(var index2 = 0; index2 < tic_tac_toe_ai_array[index].length; index2++)
            {
            next_square = next_available_square(tic_tac_toe_array, tic_tac_toe_ai_array[index][index2]);

            trial_move(tic_tac_toe_array, next_square, next_letter(tic_tac_toe_array));

            possible_outcomes[index2] = 0;

            if(win(tic_tac_toe_array, Computer_Letter()) == true)
              {
              possible_outcomes[index2] = -1 * (trial_number + 1);
              }

            if(win(tic_tac_toe_array, Player_Letter()) == true)
              {
              possible_outcomes[index2] = (trial_number * 2) - possible_player_wins;
              possible_player_wins++;
              }

            if(trial_number < 3 && turn_number + trial_number < 8 && possible_player_wins == 0)
              {
              var return_value = ai_play(tic_tac_toe_array, tic_tac_toe_ai_array, turn_number, trial_number + 1);

              if(possible_outcomes[index2] == 0)
                 possible_outcomes[index2] = return_value;

              if(return_value == -1)
                 possible_outcomes[index2] = return_value;

              if(possible_outcomes[index2] < -1 &&
                 return_value > 0)
                 possible_outcomes[index2] = return_value;

              take_back_moves(tic_tac_toe_array, turn_number + trial_number + 1);
              }

            take_back_moves(tic_tac_toe_array, turn_number + trial_number);
            }

         take_back_moves(tic_tac_toe_array, turn_number + trial_number);

         var best_choice = 0;

         if(trial_number > 0)
         for(var index2 = 0; index2 < possible_outcomes.length; index2++)
            {
            if(possible_outcomes[best_choice] == 0)
               best_choice = index2;

            //Choose the closest possible player victory, to avoid it.
            if(possible_outcomes[best_choice] > 0 &&
               possible_outcomes[index2] > 0 &&
               possible_outcomes[best_choice] > possible_outcomes[index2])
               best_choice = index2;

            //Choose possible player victories over possible computer victories, to avoid them.
            if(possible_outcomes[best_choice] < 0 &&
               possible_outcomes[index2] > 0)
               best_choice = index2;
            }
         else
         for(var index2 = 0; index2 < possible_outcomes.length; index2++)
            {
            //Dont let the player win.
            if(possible_outcomes[best_choice] > 0 &&
               possible_outcomes[index2] <= 0)
               best_choice = index2;

            //Mitigate the players possible wins.
            if(possible_outcomes[best_choice] > 0 &&
			   possible_outcomes[index2] > possible_outcomes[best_choice])
               best_choice = index2;

            //Let the computer win.
            if(possible_outcomes[index2] == -1)
               best_choice = index2;
            }

         if(trial_number == 0)
           {
           next_square = next_available_square(tic_tac_toe_array, tic_tac_toe_ai_array[index][best_choice]);
           move(tic_tac_toe_array, next_square, next_letter(tic_tac_toe_array));
           }

         take_back_moves(tic_tac_toe_array, turn_number + trial_number + 1);
         return(possible_outcomes[best_choice]);
         }

function Computer_Letter()
         {
         return(computer_letter);
         }

function Player_Letter()
         {
         return(player_letter);
         }

function play()
         {
         if(turn == Computer_Letter())
            document.tic_tac_toe.message.value = 'My turn (' + Computer_Letter() + ')';
         else
            document.tic_tac_toe.message.value = 'Your turn (' + Player_Letter() + ')';

         if(win(tic_tac_toe, Computer_Letter()) == false &&
            win(tic_tac_toe, Player_Letter()) == false &&
            tied(tic_tac_toe) == false)
           {
           if(turn == Computer_Letter())
             {
             ai_play(tic_tac_toe, ai_array, move_number(tic_tac_toe), 0);
             turn = Player_Letter();
             }

           setTimeout('play();', 1000);
           }

         if(win(tic_tac_toe, Computer_Letter()))
           {
           document.tic_tac_toe.message.value = 'I win';
           }

         if(win(tic_tac_toe, Player_Letter()))
           {
           document.tic_tac_toe.message.value = 'you win';
           }

         if(tied(tic_tac_toe))
           {
           document.tic_tac_toe.message.value = 'we tied';
           }
         }

function move_number(tic_tac_toe_array)
         {
         latest_move = 0;
         for(var index = 0; index < tic_tac_toe_array.length; index++)
            {
            if(tic_tac_toe_array[index].Play >= latest_move)
               latest_move = tic_tac_toe_array[index].Play + 1;
            }

         return(latest_move);
         }

function next_letter(tic_tac_toe_array)
         {
         last_position = 0;
         for(var index = 0; index < tic_tac_toe_array.length; index++)
            {
            if(tic_tac_toe_array[index].Play > tic_tac_toe_array[last_position].Play)
               last_position = index;
            }

         if(tic_tac_toe_array[last_position].Letter == Computer_Letter())
            return(Player_Letter());
         else
            return(Computer_Letter());
         }

function user_move(square, Letter)
         {
         if(tic_tac_toe[square].Letter == '' && turn == Player_Letter())
           {
           move(tic_tac_toe, square, Letter);
           turn = Computer_Letter();
           document.tic_tac_toe.message.value = 'My turn (' + Computer_Letter() + ')';
           }
         }

function move(tic_tac_toe_array, square, Letter)
         {
         tic_tac_toe_array[square].Letter = Letter;
         tic_tac_toe_array[square].Play = move_number(tic_tac_toe_array);

         eval('document.tic_tac_toe.square' + square + '.value = \'' + Letter + '\'');
         }

function trial_move(tic_tac_toe_array, square, Letter)
         {
         if(square < tic_tac_toe_array.length)
           {
           tic_tac_toe_array[square].Letter = Letter;
           tic_tac_toe_array[square].Play = move_number(tic_tac_toe_array);

           eval('document.tic_tac_toe.square' + square + '.value = \'' + Letter + '\'');
           }
         }

function take_back_moves(tic_tac_toe_array, Play)
         {
         for(var index = 0; index < tic_tac_toe_array.length; index++)
            {
            if(tic_tac_toe_array[index].Play >= Play)
              {
              tic_tac_toe_array[index].Letter = '';
              tic_tac_toe_array[index].Play = -1;
              eval('document.tic_tac_toe.square' + index + '.value = \'\'');
              }
            }
         }

var ai_array;
var tic_tac_toe;
var turn;
var computer_letter;
var player_letter;

function new_game()
         {
         if(Math.random() < 0.5)
           {
           computer_letter = 'x';
           player_letter = 'o';
           }
         else
           {
           computer_letter = 'o';
           player_letter = 'x';
           }

         if(Math.random() < 0.5)
            turn = Computer_Letter();
         else
            turn = Player_Letter();

         randomise_ai_array(ai_array);

         take_back_moves(tic_tac_toe, 0);
         }

function init()
         {
         ai_array = create_tic_tac_toe_ai_array();
         tic_tac_toe = create_tic_tac_toe_array();

         new_game();

         play();
         }

function win(tic_tac_toe_array, Letter)
         {
         //First row, first column, and diagonal.
         if(tic_tac_toe_array[0].Letter == Letter)
           {
           if(tic_tac_toe_array[1].Letter == Letter && tic_tac_toe_array[2].Letter == Letter)
              return(true);
           if(tic_tac_toe_array[3].Letter == Letter && tic_tac_toe_array[6].Letter == Letter)
              return(true);
           if(tic_tac_toe_array[4].Letter == Letter && tic_tac_toe_array[8].Letter == Letter)
              return(true);
           }

         //Second row, second column, and other diagonal.
         if(tic_tac_toe_array[4].Letter == Letter)
           {
           if(tic_tac_toe_array[3].Letter == Letter && tic_tac_toe_array[5].Letter == Letter)
              return(true);
           if(tic_tac_toe_array[1].Letter == Letter && tic_tac_toe_array[7].Letter == Letter)
              return(true);
           if(tic_tac_toe_array[2].Letter == Letter && tic_tac_toe_array[6].Letter == Letter)
              return(true);
           }

         //Third row and third column.
         if(tic_tac_toe_array[8].Letter == Letter)
           {
           if(tic_tac_toe_array[6].Letter == Letter && tic_tac_toe_array[7].Letter == Letter)
              return(true);
           if(tic_tac_toe_array[2].Letter == Letter && tic_tac_toe_array[5].Letter == Letter)
              return(true);
           }

         return(false);
         }

function tied(tic_tac_toe_array)
         {
         if(win(tic_tac_toe_array, Player_Letter()) == false &&
            win(tic_tac_toe_array, Computer_Letter()) == false)
           {
            for(var index = 0; index < tic_tac_toe_array.length; index++)
                if(tic_tac_toe_array[index].Letter == '')
                   return(false);

           return(true);
           }

         return(false);
         }
</script>
</head>

<body onload="init();">

<form name="tic_tac_toe">
<table>
<tr>
<td colspan="3" align="center">
<input type="text" size="9" name="message" style="border:none; text-align:center;" /></td>
</tr>

<tr>
<td>
<input type="text" size="5" name="square0" readonly
       onclick="user_move(0, Player_Letter());" /></td>
<td align="center">
<input type="text" size="5" name="square1" readonly
       onclick="user_move(1, Player_Letter());" /></td>
<td align="right">
<input type="text" size="5" name="square2" readonly
       onclick="user_move(2, Player_Letter());" /></td>
</tr>

<tr>
<td>
<input type="text" size="5" name="square3" readonly
       onclick="user_move(3, Player_Letter());" /></td>
<td align="center">
<input type="text" size="5" name="square4" readonly
       onclick="user_move(4, Player_Letter());" /></td>
<td align="right">
<input type="text" size="5" name="square5" readonly
       onclick="user_move(5, Player_Letter());" /></td>
</tr>

<tr>
<td>
<input type="text" size="5" name="square6" readonly
       onclick="user_move(6, Player_Letter());" /></td>
<td align="center">
<input type="text" size="5" name="square7" readonly
       onclick="user_move(7, Player_Letter());" /></td>
<td align="right">
<input type="text" size="5" name="square8" readonly
       onclick="user_move(8, Player_Letter());"  /></td>
</tr>

<tr>
<td colspan="3"><input type="button" value="new game"
                       onclick="new_game();
                                play();" /></td>
</tr>
</table>

<input type="checkbox" name="debug_switch" />
</form>
</body>
</html>
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