The Friday Fragment

It’s Friday, and time again for the Friday Fragment: our weekly programming-related puzzle.

This Week’s Fragment

Even T-Rex likes to code games that play themselves, so let’s continue with our Reversi “game bot:”

Write code to call competing Reversi bots, flip pieces, and score the results.  If you’d like, you can build atop the solution we used for tic-tac-toe.

To “play along,” provide either the URL or the code for the solution. You can post it as a comment or send it via email.

Last Week’s Fragment – Solution

Last week’s puzzle was to start a Reversi (a.k.a., Othello) “bot:”

Code a simple REST web service to start playing Reversi.  It should accept a 64-character string representing the current 8×8 “game board” with dot (empty space), X (black), or O (white) in each position (starting from the top left, going left-to-right and down).  It should return a 64-character string with your next move added.   Don’t worry about turning pieces yet, just find the next best move.

Here’s a simple solution in PHP, with room for improvement.  To start playing, pass it ?board=………………………OX……XO………………………&piece=X.

<?php
  if (!ereg('^[XO.]{64}$', $board=$_REQUEST['board']))
    die(str_repeat('X',64));
  if (!ereg('^[XO]$', $mypiece=$_REQUEST['piece']))
    die(str_repeat('.',64));

  if (!is_null($result = find_move($board, $mypiece)))
    exit($result);
  else
    exit($board);

  function find_move($board, $piece) {

    STATIC $plays = array( 0, 7, 56, 63,                  // outer corners
                           2, 5, 16, 23, 40, 47, 58, 61,  // A-squares
                           3, 4, 24, 32, 31, 39, 59, 60,  // B-squares
                          18, 21, 42, 45,                 // inner corners
                          19, 20, 26, 29, 34, 37, 43, 44, // inner sides
                          10, 11, 12, 13, 17, 22, 25, 30, // mid sides
                          33, 38, 41, 46, 50, 51, 52, 53,
                           1, 6, 8, 15, 48, 55, 57, 62,   // C-squares
                           9, 14, 49, 54 );               // X-squares              

    foreach ($plays as $play)
      if ($board[$play] == '.' && can_play($board, $piece, $play)) {
        $board[$play] = $piece;
        return $board;
      }
    return null;
  }
?>

Of course, there are much smarter ways to code Reversi, such as applying common strategies and running look-ahead scenarios, but that’d be more than a fragment.  Years ago, a coworker wrote one for VisualWorks (still in the Cincom Public Repository), and there’s a well-documented implementation at lurgee.net.  If you’re up for coding a smarter version behind the service interface, give it a shot.

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