//Q-learning 源码分析。 
import java.util.Random;

public class QLearning1
{
    private static final int Q_SIZE = 6;
    private static final double GAMMA = 0.8;
    private static final int ITERATIONS = 10;
    private static final int INITIAL_STATES[] = new int[] {1, 3, 5, 2, 4, 0};

    private static final int R[][] = new int[][] {{-1, -1, -1, -1, 0, -1}, 
                                                  {-1, -1, -1, 0, -1, 100}, 
                                                  {-1, -1, -1, 0, -1, -1}, 
                                                  {-1, 0, 0, -1, 0, -1}, 
                                                  {0, -1, -1, 0, -1, 100}, 
                                                  {-1, 0, -1, -1, 0, 100}};

    private static int q[][] = new int[Q_SIZE][Q_SIZE];
    private static int currentState = 0;
    
    private static void train()
    {
        initialize();

        // Perform training, starting at all initial states.
        for(int j = 0; j < ITERATIONS; j++)
        {
            for(int i = 0; i < Q_SIZE; i++)
            {
                episode(INITIAL_STATES[i]);
            } // i
        } // j

        System.out.println("Q Matrix values:");
        for(int i = 0; i < Q_SIZE; i++)
        {
            for(int j = 0; j < Q_SIZE; j++)
            {
                System.out.print(q[i][j] + ",\t");
            } // j
            System.out.print("\n");
        } // i
        System.out.print("\n");

        return;
    }
    
    private static void test()
    {
        // Perform tests, starting at all initial states.
        System.out.println("Shortest routes from initial states:");
        for(int i = 0; i < Q_SIZE; i++)
        {
            currentState = INITIAL_STATES[i];
            int newState = 0;
            do
            {
                newState = maximum(currentState, true);
                System.out.print(currentState + ", ");
                currentState = newState;
            }while(currentState < 5);
            System.out.print("5\n");
        }

        return;
    }
    
    private static void episode(final int initialState)
    {
        currentState = initialState;

        // Travel from state to state until goal state is reached.
        do
        {
            chooseAnAction();
        }while(currentState == 5);

        // When currentState = 5, Run through the set once more for convergence.
        for(int i = 0; i < Q_SIZE; i++)
        {
            chooseAnAction();
        }
        return;
    }
    
    private static void chooseAnAction()
    {
        int possibleAction = 0;

        // Randomly choose a possible action connected to the current state.
        possibleAction = getRandomAction(Q_SIZE);

        if(R[currentState][possibleAction] >= 0){
            q[currentState][possibleAction] = reward(possibleAction);
            currentState = possibleAction;
        }
        return;
    }
    
    private static int getRandomAction(final int upperBound)
    {
        int action = 0;
        boolean choiceIsValid = false;

        // Randomly choose a possible action connected to the current state.
        while(choiceIsValid == false)
        {
            // Get a random value between 0(inclusive) and 6(exclusive).
            action = new Random().nextInt(upperBound);
            if(R[currentState][action] > -1){
                choiceIsValid = true;
            }
        }

        return action;
    }
    
    private static void initialize()
    {
        for(int i = 0; i < Q_SIZE; i++)
        {
            for(int j = 0; j < Q_SIZE; j++)
            {
                q[i][j] = 0;
            } // j
        } // i
        return;
    }
    
    private static int maximum(final int State, final boolean ReturnIndexOnly)
    {
        // If ReturnIndexOnly = True, the Q matrix index is returned.
        // If ReturnIndexOnly = False, the Q matrix value is returned.
        int winner = 0;
        boolean foundNewWinner = false;
        boolean done = false;

        while(!done)
        {
            foundNewWinner = false;
            for(int i = 0; i < Q_SIZE; i++)
            {
                if(i != winner){             // Avoid self-comparison.
                    if(q[State][i] > q[State][winner]){
                        winner = i;
                        foundNewWinner = true;
                    }
                }
            }

            if(foundNewWinner == false){
                done = true;
            }
        }

        if(ReturnIndexOnly == true){
            return winner;
        }else{
            return q[State][winner];
        }
    }
    
    private static int reward(final int Action)
    {
        return (int)(R[currentState][Action] + (GAMMA * maximum(Action, false)));
    }
    
    public static void main(String[] args)
    {
        train();
        test();
        return;
    }

}

Reinforcement Learning Q-learning 算法学习-3