Java在数组中搜索重复模式

Question

I have a program that is searching a maze to find the best way out. As it searches it adds the next move to an array. My problem is that it keeps repeating the same three moves over and over. I need to find the best way to check that array of moves in order to force it to change move when a loop has been detected.

edit for clarity, http://www.logicmazes.com/theseus.html maze three is the one I'm testing. what happens is that it gets stuck moving up and down in the column it starts in.

Answer 1

You could keep track of every cell your current path has already visited, and not go to those cells again (since that would create a loop).

As far as the data structure is concerned, I see two main possibilities:

• keep an array -- or a set -- of coordinates that you've visited; or
• have a boolean array of the same dimensions as the maze, setting the visited cells to true .

You would need to update the structure whenever you take a step, and whenever you backtrack.

Answer 2

If you are using an Array then you should be able to use "contains" method to check if the move is already in the array.

In order to do that you may have to modify your equals method to compare two different moves to check if they are the same.

In that case, when you identify the same move, you can ignore that and look for other moves. An example pseudo code

public class Move {
  int x;
  int y;

  public boolean equals(Object o){
    if(o == null) return false;
    if(!(o instanceof) Move) return false;

    Move other = (Move) o;
    if(this.x != other.x) return false;
    if(this.y != other.y)   return false;

    return true;
  }
}

public class SolveMaze {
    List<Move> moves;
    ...
    public boolean isValidMove(Move move) {
        if (moves.contains(move)) return false;
        else {
            ...
                moves.add(move);
        }
    }
}

Answer 3

It sounds like the problem is that your "state" doesn't actually contain enough state information. In every cycle, after Theseus has moved and the Minotaur has moved twice, the state consists of the following:

• Theseus's x-coordinate.
• Theseus's y-coordinate.
• The Minotaur's x-coordinate.
• The Minotaur's y-coordinate.

You can represent these as some sort of MazeState object whose equals and hashCode methods make it easy to see if two instances represent the same state.

Since the Minotaur's motion follows a very rigid program, every move that Theseus makes (left/right/up/down/delay) will move from one well-defined state to another. You then need to forbid Theseus from making any moves that:

• Would cause the Minotaur's x- and y-coordinates to equal those of Theseus (since this means Theseus is dead).
• Would cause the new state to be equal to a state that you've previously been in (since this means that no progress has been made).

To do this, you can store the previous states in a HashSet<MazeState> .