src/libttc-pplayer.rb

   1 # == Synopsis
   2 #
   3 # Library to support a Trap the Cap player that uses potentials to select the
   4 # best move
   5 #
   6 # == Author
   7 # Neil Smith
   8 #
   9 # == Change history
  10 # Version 1.1::  23 April 2008
  11
  12 require 'libttc'
  13
  14 # Play Trap the Cap by using potential fields.  For each possible move,
  15 # calculate the field strength and pick the move with the lowest potential
  16 class Potential_player
  17
  18   attr_reader :friend_pull, :enemy_pull, :base_pull,
  19     :safe_bonus, :capture_bonus
  20
  21   def initialize(args, verbose = false)
  22     @friend_pull   = args[:friend_pull]   || 1
  23     @enemy_pull    = args[:enemy_pull]    || 0.5
  24     @base_pull     = args[:base_pull]     || 2
  25     @safe_bonus    = args[:safe_bonus]    || 8
  26     @capture_bonus = args[:capture_bonus] || 10
  27
  28     @verbose = verbose
  29   end
  30
  31   # Find the best move of the possible ones
  32   def best_move(game, die_result)
  33     me = game.current_player
  34     possible_moves = game.possible_moves(die_result, me)
  35     scored_moves = possible_moves.collect do |m|
  36       begin
  37         game.apply_move! m
  38         score = score_position(game, me)
  39 #        game.undo_move!
  40       rescue GameWonNotice
  41         score = 10000
  42       ensure
  43         game.undo_move!
  44       end
  45       puts "#{m} scores #{score}" if @verbose
  46       [m, score]
  47     end
  48     best_move = (scored_moves.max {|a, b| a[1] <=> b[1]})[0]
  49   end
  50
  51   # Calculate the potential score of a position for a given player
  52   def score_position(game, player)
  53     score = 0
  54     game.pieces.each_value do |piece|
  55       here = piece.position
  56       if piece.colour == player
  57         game.pieces.each_value do |other_piece|
  58           if other_piece.colour == player
  59             score += game.board.distance_between[here.place][other_piece.position.place] * @friend_pull
  60           else
  61             score += game.board.distance_between[here.place][other_piece.position.place] * @enemy_pull
  62           end
  63         end
  64         score += piece.contains.length * @capture_bonus
  65         score += game.board.distance_between[here.place][game.board.positions[player].place] *
  66         piece.contains.length * @base_pull
  67       elsif here == game.board.positions[player]
  68         score += @safe_bonus
  69       end
  70     end
  71     score
  72   end
  73
  74 end