我目前正在使用A *算法（汉明）方法实现八难题，并提供了代码：
public class Board
{
int board[][];
public Board()
{
board = new int[3][3];
}
public void initialise(int n1, int n2, int n3, int n4, int n5, int n6, int n7, int n8, int n9)
{
//first row
board[0][0] = n1;
board[0][1] = n2;
board[0][2] = n3;
//second row
board[1][0] = n4;
board[1][1] = n5;
board[1][2] = n6;
//third row
board[2][0] = n7;
board[2][1] = n8;
board[2][2] = n9;
}
public int states_out_of_order()
{
int count = 0;
for(int i = 0; i < 3; i++)
{
//Checking if first row is
//1 2 3
if(i==0)
{
if(board[i][0]!=1)
{
count++;
}
if(board[i][1]!=2)
{
count++;
}
if(board[i][2]!=3)
{
count++;
}
}
//Checking if second row is
//4 5 6
if(i==1)
{
if(board[i][0]!=4)
{
count++;
}
if(board[i][1]!=5)
{
count++;
}
if(board[i][2]!=6)
{
count++;
}
}
//Checking if second row is
//7 8 0
if(i==2)
{
if(board[i][0]!=7)
{
count++;
}
if(board[i][1]!=8)
{
count++;
}
if(board[i][2]!=9)
{
count++;
}
}
}
return count;
}
public boolean GoalStateCheck()
{
//Checking first row
if(board[0][0]!=1)
{
return false;
}
if(board[0][1]!=2)
{
return false;
}
if(board[0][2]!=3)
{
return false;
}
//Checking second row
if(board[1][0]!=4)
{
return false;
}
if(board[1][1]!=5)
{
return false;
}
if(board[1][2]!=6)
{
return false;
}
//Checking third row
if(board[2][0]!=7)
{
return false;
}
if(board[2][1]!=8)
{
return false;
}
if(board[2][2]!=0)
{
return false;
}
return true;
}
public void printBoard()
{
System.out.print(board[0][0] + " " + board[0][1] + " " + board[0][2]);
System.out.println();
System.out.print(board[1][0] + " " + board[1][1] + " " + board[1][2]);
System.out.println();
System.out.print(board[2][0] + " " + board[2][1] + " " + board[2][2]);
System.out.println();
}
}
现在解算器类
import java.util.ArrayList;
public class Solver
{
ArrayList<Board> list;
int steps;
public Solver()
{
list = new ArrayList<Board>();
steps = 0;
}
public Board SwapStates(Board b, int a[][], int r1, int c1, int r2, int c2)
{
int temp = a[r1][c1];
a[r1][c1] = a[r2][c2];
a[r2][c2] = temp;
return b;
}
//Find the board in ArrayList according the number of states out of order
public Board findBoard(int num)
{
for(int i = 0; i < list.size(); i++)
{
if(num == list.get(i).states_out_of_order())
{
return list.get(i);
}
}
return null;
}
//Choose the puzzle state with minimum states that are out of order
public int min()
{
int n = 10;
for(int i = 0; i < list.size(); i++)
{
if(list.get(i).states_out_of_order() < n)
{
n = list.get(i).states_out_of_order();
}
}
return n;
}
//Find the board in ArrayList and remove it
public void matchRemove(Board b)
{
for(int i = 0; i < list.size(); i++)
{
if(b == list.get(i))
{
list.remove(list.get(i));
break;
}
}
}
public void Hamming(Board b)
{
boolean solved = b.GoalStateCheck();
while(!solved)
{
if(b.board[0][0] == 0)
{
//Pointer to original board
final Board ptr = b;
Board b1 = ptr;
Board b2 = ptr;
//Check move #1 from original state
b1 = SwapStates(b1, b1.board,0,0,0,1);
//Check move #2 from original state
//Problem is that it is not swapping ptr but rather its swapping b1. why?
b2 = SwapStates(b2, b2.board,0,0,1,0);
//Add the moves to the Arraylist
list.add(b1);
list.add(b2);
//Find the board with minimum number of states out of order and remove it frm list
int n = min();
Board temp = findBoard(n);
matchRemove(temp);
//Assign removed board as optimum move
b = temp;
steps++;
b.printBoard();
}
else if(b.board[0][1] == 0)
{
}
else if(b.board[0][2] == 0)
{
}
else if(b.board[1][0] == 0)
{
}
else if(b.board[1][1] == 0)
{
}
else if(b.board[1][2] == 0)
{
}
else if(b.board[2][0] == 0)
{
}
else if(b.board[2][1] == 0)
{
}
else if(b.board[2][2] == 0)
{
}
else
{
System.out.println("Board is not in its proper form");
break;
}
}
/*System.out.println("Goal State has been achieved!!");
System.out.println("It took " + steps + " moves");
b.printBoard();*/
}
}
在我的Solver类的Hamming函数中，在第一个if语句中我有这一行
final Board ptr = b;
Board b1 = ptr;
Board b2 = ptr;
然而，在这两行：
//Check move #1 from original state
b1 = SwapStates(b1, b1.board,0,0,0,1);
//Check move #2 from original state
//Problem is that it is not swapping ptr but rather its swapping b1. why?
b2 = SwapStates(b2, b2.board,0,0,1,0);
b2正在使用b1的交换状态而不是我想要使用的原始ptr。为什么呢？
答案 0 :(得分：1)
当你写完
final Board ptr = b;
Board b1 = ptr;
Board b2 = ptr;
您没有创建名为b的{{1}}的不可变副本以及名为ptr和ptr的{{1}}的两个可变副本}。
您只需创建3个对同一对象的引用。使用任何4个引用对对象进行的任何修改都将以相同的方式影响对象，从而更改所有4个引用的可见状态。
你应该做的是在你的棋盘类中添加一个b1方法，它会返回另一个Board实例（使用b2并复制值）并通过以下方式更改你的代码：
public Board copy()