Question

我试图通过首先将棋盘添加到队列然后以最小汉明距离将一个状态出列来解决8-puzzle问题。我有功能，但我无法找到它们是否工作，因为我在第26行得到一个空指针异常。

package ai8puzzle;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.PriorityQueue;

/**
 *
 * @author Dell Inspiron
 */
public class My8Puzzle  {
    static int[] board={0,1,3,4,2,5,7,8,6};
        static int[] goal={1,2,3,4,5,6,7,8,0};
    public static void main(String[] args){

        int h;
        h = CalcHamming(board, goal);
        int prev_h = getHole();
        PriorityQueue<int[]> q = null;
        int[] b= {0,1,3,4,2,5,7,8,6};
        q.add(b);    //null pointer exception here

        while(h!=0){
            ArrayList<int[]> g;
            g = genSuccessors();
           for (int i=0; i<g.size(); i++){
               if(!q.contains(g.get(i)))
               q.offer(g.get(i));
           }
           System.out.println("board: "+Arrays.toString(q.poll()));

        }


    }

    public static ArrayList<int[]> genSuccessors()
    {
        ArrayList<int[]> successors = new ArrayList<>();
        int hole = getHole();

        // try to generate a state by sliding a tile leftwise into the hole
        // if we CAN slide into the hole
        if (hole != 0 && hole != 3 && hole != 6)
        {
            /*
             * we can slide leftwise into the hole, so generate a new state for
             * this condition and throw it into successors
             */
            swapAndStore(hole - 1, hole, successors);
        }

        // try to generate a state by sliding a tile topwise into the hole
        if (hole != 6 && hole != 7 && hole != 8)
        {
            swapAndStore(hole + 3, hole, successors);
        }

        // try to generate a state by sliding a tile bottomwise into the hole
        if (hole != 0 && hole != 1 && hole != 2)
        {
            swapAndStore(hole - 3, hole, successors);
        }
        // try to generate a state by sliding a tile rightwise into the hole
        if (hole != 2 && hole != 5 && hole != 8)
        {
            swapAndStore(hole + 1, hole, successors);
        }

        return successors;
    }

    /*
     * Switches the data at indices d1 and d2, in a copy of the current board
     * creates a new state based on this new board and pushes into s.
     */
    public static void swapAndStore(int d1, int d2, ArrayList<int[]> s)
    {
        int[] cpy = copyBoard(board);
        int temp = cpy[d1];
        cpy[d1] = board[d2];
        cpy[d2] = temp;
        s.add(cpy);

    }
        public static  int[] copyBoard(int[] state)
    {
        int[] ret = new int[9];
        System.arraycopy(state, 0, ret, 0, 9);
        return ret;
    }
    private static int CalcHamming(int[] b, int[] g) {
        int h=0;

            for(int j=0; j<9; j++){
                if(b[j]!=g[j]){
                    h++;
                }
            }

        return h; //To change body of generated methods, choose Tools | Templates.
    }

    private static int getHole() {
         int h=0;
            for(int j=0; j<3; j++){
                if(board[j]==0){
                    h=j;
                }
            }

        return h;
    }


}

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Answer 1

在向其添加元素之前，您必须初始化PriorityQueue<int[]> q：

    PriorityQueue<int[]> q = new PriorityQueue<int[]>();
    int[] b= {0,1,3,4,2,5,7,8,6};
    q.add(b);

如果PriorityQueue是接口，则必须使用兼容的实现进行初始化。

尝试使用java队列解决8个难题

1 个答案: