Question

我知道之前已经问过这个问题，但我根本看不出答案。我应该写递归迷宫解决方案，这是我到目前为止所做的：

import java.awt.Color;
import java.util.ArrayList;

public class RecursiveMazeSolution implements MazeSolver {
boolean[][] marked;
ArrayList<Maze.Door> solutionPath = new ArrayList<>();

public ArrayList<Maze.Door> solveMaze(int startRow, int finishRow, int startCol, int finishCol, Maze maze) {
    marked = new boolean[maze.getRows()][maze.getColumns()];
    return solveMaze(startRow, finishRow, startCol, finishCol, maze, marked);
}

public ArrayList<Maze.Door> solveMaze(int startRow, int finishRow, int startCol, int finishCol, Maze maze, boolean[][] marked) {
    System.out.println(startRow + " " + startCol + " " + finishRow + " " + finishCol);
    if(startRow < 0 || startCol < 0 || startRow > maze.getRows() - 1|| startCol > maze.getColumns() - 1) return null;
    if(marked[startRow][startCol]) {
        System.out.println("I'm inside marked if");
        return null;
    }

    marked[startRow][startCol] = true;
    if(startRow == finishRow && startCol == finishCol) {
        solutionPath.add(new Maze.Door(startRow, startCol, Maze.NO_DIRECTION, Color.RED));
        return solutionPath;
    }

    if(solveMaze(startRow - 1, finishRow, startCol, finishCol,maze, marked) != null && !maze.isClosed(startRow, startCol, Maze.NORTH)) {
        solutionPath.add(new Maze.Door(startRow, startCol, Maze.NORTH, Color.RED));
        return solutionPath;
    }
    if(solveMaze(startRow + 1, finishRow, startCol, finishCol,maze, marked) != null && !maze.isClosed(startRow, startCol, Maze.SOUTH)){
        solutionPath.add(new Maze.Door(startRow, startCol, Maze.SOUTH, Color.RED));
        return solutionPath;
    }
    if(solveMaze(startRow, finishRow, startCol - 1, finishCol,maze, marked) != null && !maze.isClosed(startRow, startCol, Maze.WEST)){
        solutionPath.add(new Maze.Door(startRow, startCol, Maze.WEST, Color.RED));
        return solutionPath;
    }
    if(solveMaze(startRow, finishRow, startCol + 1, finishCol,maze, marked) != null && !maze.isClosed(startRow, startCol, Maze.EAST)){
        solutionPath.add(new Maze.Door(startRow, startCol, Maze.EAST, Color.RED));
        return solutionPath;
    }

    return null;
}


}

以下是提供给我的迷宫课程：

import java.io.Serializable;
import java.awt.Color;

public class Maze implements Serializable {

/**
 * 
 */
private static final long serialVersionUID = -787488019846627488L;
/**
 * the north wall of a room
 */
public static final int NORTH = 0;
/**
 * the east wall of a room
 */
public static final int EAST = 1;
/**
 * the south wall of a room
 */
public static final int SOUTH = 2;
/**
 * the west wall of a room
 */
public static final int WEST = 3;
/**
 * No direction from a room
 */
public static final int NO_DIRECTION = 4;
private static String[] walls = {"North", "East", "South", "West"};
private Room[][] rooms;

/**
 * Constructor
 * @param rows is the number of rows in the maze
 * @param columns is the number of columns in the maze
 */
public Maze(int rows, int columns) {
    rooms = new Room[rows][columns];
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < columns; j++) {
            rooms[i][j] = new Room();
        } // end for
    } // end for
}

/**
 * rows accessor
 * @return the number of rows in the maze
 */
public int getRows() {
    return rooms.length;
}

/**
 * columns accessor
 * @return the number of columns in the maze
 */
public int getColumns() {
    return rooms[0].length;
}

/**
 * Checks to see if a wall is closed
 * @param row the row number
 * @param column the column number
 * @param wall the wall number
 * @return true if wall is closed; false if it is open
 */
public boolean isClosed(int row, int column, int wall) {
    return rooms[row][column].closed[wall];
}

/**
 * Opens the wall
 * @param row the row number
 * @param column the column number
 * @param wall the wall number
 */
public void setOpen(int row, int column, int wall) {
    rooms[row][column].closed[wall] = false;
}

/**
 * Closes the wall
 * @param row the row number
 * @param column the column number
 * @param wall the wall number
 */
public void setClosed(int row, int column, int wall) {
    rooms[row][column].closed[wall] = true;
}

public static class Door {

    int row;
    int column;
    int wall;
    Color color;

    public Door(int row, int column, int wall, Color color) {
        this.row = row;
        this.column = column;
        this.wall = wall;
        this.color = color;
    } // end constructor

    public boolean equals(Object x) {
        if ( x == null ) return false;
        if (!(x.getClass().equals(this.getClass()))) {
            return false;
        }
        Door door = (Door) x;
        return row == door.row && column == door.column && wall == door.wall && color.equals(door.color);
    } // end equal

    public int hashCode() {
        return row + column + wall + color.hashCode();
    }

    public String toString() {
        return row + " " + column + " " + walls[wall] + "\n";
    } // end toString()
} // end Door

private class Room implements Serializable {

    boolean[] closed;

    Room() {
        closed = new boolean[4];
        for (int i = 0; i < 4; i++) {
            closed[i] = true;
        } // end for
    }
} // end Room
} // end Maze

我认为我的解决方案正确，但我的程序只是递归运行了一段时间，然后找不到迷宫的解决方案。此外，如果我让我的程序忽略“墙”，它可以找到一个解决方案（在很多递归调用之后），但它不应该忽略墙。谁能告诉我我做错了什么？

Answer 1

根据您的代码快速浏览一下，我认为问题在于您不会在solveMaze中取消标记访问过的广场。当您输入该功能时，您标记一个方块，表示您无法再次访问它。但是你需要在返回之前再将其标记为免费。

在考虑了这一点之后，似乎通常不会出现问题，因为在确定通过该方块没有解决方案路径后，您将取消标记方格。

然后我意识到你在递归调用之后正在进行墙测试。这意味着你正在通过墙壁寻找解决方案，然后放弃解决方案，因为路上有一堵墙。与此同时，您将所有正方形标记为已访问，并且无处可寻找有效的解决方案。

您需要在递归之前测试墙，如果有墙，则不要进行递归。此处的短路评估应该足够了（通过重新排序if语句中的术语）：

if( !maze.isClosed(startRow, startCol, Maze.NORTH) && solveMaze(startRow-1, finishRow, startCol, finishCol,maze, marked) != null )

顺便说一句，没有必要将marked作为参数传递。它是集体成员。

递归地解决迷宫

1 个答案: