public State GetNextState(State currentState, JointAction action)
{
var possibleStates = _transitionTable[new ProbabilityTransitionKey(currentState, action)];
return(possibleStates[_random.Next(possibleStates.Count)]);
}
private void AddNextStateProbabilities(State currentState, JointAction action)
{
var possibleNextStates = new List <State>();
var nextPlayerAPosition = GetNextPosition(currentState.PlayerAPosition, action.CurrentPlayerAction);
var nextPlayerBPosition = GetNextPosition(currentState.PlayerBPosition, action.OpposingPlayerAction);
//"When a player executes an action that would take it to the square occupied by the other player, possession of
// the ball goes to the stationary player and the move does not take place"
// Player A goes first and runs into player B's current position
// or Player B goes first and runs into player A's position
// "If the sequences of actions causes the players to collide, then only the first moves"
if (nextPlayerAPosition == currentState.PlayerBPosition && nextPlayerBPosition == currentState.PlayerAPosition)
{
//50% chance that the player with the ball moves first in this scenario, and nobody moves. As such, 50% chance the possession is changed to the other player.
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.A));
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.B));
}
//The second move will result in a collision. Only the first move takes place and ball changes possession only if the second player possesses the ball
else if (nextPlayerAPosition == nextPlayerBPosition)
{
possibleNextStates.Add(new State(currentState.PlayerAPosition, nextPlayerBPosition, BallPossessor.B));
possibleNextStates.Add(new State(nextPlayerAPosition, currentState.PlayerBPosition, BallPossessor.A));
}
else if (nextPlayerAPosition == currentState.PlayerBPosition && nextPlayerBPosition != currentState.PlayerAPosition)
{
if (currentState.Possessor == BallPossessor.A)
{
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.B));
}
else
{
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.A));
}
possibleNextStates.Add(new State(nextPlayerAPosition, nextPlayerBPosition, currentState.Possessor));
}
else if (nextPlayerAPosition != currentState.PlayerBPosition && nextPlayerBPosition == currentState.PlayerAPosition)
{
if (currentState.Possessor == BallPossessor.B)
{
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.A));
}
else
{
possibleNextStates.Add(new State(currentState.PlayerAPosition, currentState.PlayerBPosition, BallPossessor.B));
}
possibleNextStates.Add(new State(nextPlayerAPosition, nextPlayerBPosition, currentState.Possessor));
}
//No collision took place, deterministically move the players to their next locations
else
{
possibleNextStates.Add(new State(nextPlayerAPosition, nextPlayerBPosition, currentState.Possessor));
}
possibleNextStates.RemoveAll(s => s.PlayerAPosition == s.PlayerBPosition);
_transitionTable[new ProbabilityTransitionKey(currentState, action)] = possibleNextStates;
}
public ProbabilityTransitionKey(State currentState, JointAction action)
{
CurrentState = currentState;
Action = action;
}
