【发布时间】：2013-11-11 21:18:11
【问题描述】：
我正在创建一个深度优先搜索算法，该算法最终将能够解决一个简单的 8 难题。我能够读取文件和目标状态并相应地设置这些变量。
我收到的主要问题是，当我对当前节点的子节点进行评估时，我在我的 8 拼图中得到了 2 个“空”值，而且我还得到了一个索引越界异常。
为了获得给定父节点的子节点，我首先必须进行有效移动，然后更新子节点的状态以反映有效移动的结果。
为了执行移动，我检查它是否可行（如果我向左移动它仍然在拼图的范围内），请参阅发布的代码。
当它正确打印预期结果时，它在前 2 个移动（左右移动）中正常运行。
下面是我当前代码执行的输出，你可以看到它正确地左右移动，然后它开始遇到错误。
Start state:
120
345
678
after moving left
102
345
678
Parent: [[C@1b845568
after moving down
125
340
678
Parent: [[C@d032cf5
after moving left
102
340
678
Parent: [[C@d032cf5
after moving down
125
348
670
Parent:
125
340
678
after moving up
125
348
670
Parent: [[C@4b7c8f7f
after moving left
125
304
670
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 3
at dcs.aber.ac.uk.puzzle.PuzzleBoard.swapValues(PuzzleBoard.java:193)
at dcs.aber.ac.uk.puzzle.PuzzleBoard.moveUp(PuzzleBoard.java:142)
at dcs.aber.ac.uk.puzzle.DFSSolver.addChildren(DFSSolver.java:155)
at dcs.aber.ac.uk.puzzle.DFSSolver.search(DFSSolver.java:85)
at dcs.aber.ac.uk.puzzle.DFSSolver.<init>(DFSSolver.java:27)
at dcs.aber.ac.uk.puzzle.Driver.main(Driver.java:86)
如您所见，在前两个之后，其余的打印状态都不正确。我将发布我的代码来展示我如何处理板的交换和更新，看看你是否能确定出现问题的地方。
public class Node {
private Node parent;
private char[][] state = new char[3][3];
private double cost;
private double heurCost;
private double funcCost;
private int depth;
public Node() {
parent = null;
}
public Node(Node parent) {
this.parent = parent;
for(int i = 0; i < 3; i++){
for(int j = 0; j< 3; j++){
state[i][j] = parent.getState()[i][j];
}
}
}
public void setParent(Node parent) {
this.parent = parent;
}
public char[][] getState() {
return state;
}
public char[][] copyState(){
char[][] a = new char[3][3];
for(int i = 0; i < 3; i++){
for(int j = 0; j< 3; j++){
a[i][j] = state[i][j];
}
}
return a;
}
}
public class PuzzleBoard {
private char[][] goalState;
private char[][] currentBoard;
private int emptyRow, emptyCol;
private int outOfPlace;
public PuzzleBoard(char[][] currentState, char[][] goal ){
this.setCurrentState(currentState);
this.setGoalState(goal);
trackEmptySqaure();
}
public void setGoalState(char[][] goalState){
this.goalState = goalState;
}
public void setCurrentState(char[][] currentState){
this.currentBoard = currentState;
}
public char[][] getCurrentBoard() {
return currentBoard;
}
public boolean checkIsGoal(char[][] board){
for(int i = 0; i < 9; i ++){
for(int j = 0; j < 3; j ++){
if(!(goalState[i][j] != (board[i][j]))){
return false;
}
}
}
return true;
}
public void trackEmptySqaure() {
for(int i = 0; i < 3; i ++){
for (int j = 0; j < 3; j ++){
if(currentBoard[i][j] == '0'){
emptyCol = j;
emptyRow = i;
}
}
}
}
public int getemptyRow() {
return emptyRow;
}
public int getemptyCol() {
return emptyCol;
}
public Node moveLeft(Node parent){
currentBoard = parent.copyState();
Node result = new Node(parent);
/* check you can move 'empty' left one space*/
if(getemptyCol() > 0){
swapValues(result.getState(),emptyRow, emptyCol, 1);
return result;
}
return null;
}
public Node moveDown(Node parent){
currentBoard = parent.copyState();
Node result = new Node(parent);
/* check you can move 'empty' down one space*/
if(getemptyRow() < 2){
swapValues(result.getState(),emptyRow, emptyCol,2);
return result;
}
return null;
}
public Node moveUp(Node parent){
currentBoard = parent.getState();
Node result = new Node(parent);
/* check you can move 'empty' up one space*/
if(getemptyRow() > 0){
swapValues(result.getState(),emptyRow, emptyCol,2);
return result;
}
return null;
}
public Node moveRight(Node parent){
currentBoard = parent.getState();
Node result = new Node(parent);
/* check you can move 'empty' right one space*/
if(getemptyCol() < 2){
swapValues(result.getState(),emptyRow, emptyCol,2);
return result;
}
return null;
}
public void swapValues (char[][] c,int x, int y, int method){
char empty = '0';
char swapValue = '0'; // should never be kept as 0
if(method == 1){ // left
swapValue= c[emptyRow][emptyCol -1];
c[emptyRow][emptyCol] = swapValue;
c[emptyRow][emptyCol -1] = empty;
trackEmptySqaure();
}
else if(method == 2){ // down
swapValue = c[emptyRow + 1][emptyCol];
c[emptyRow][emptyCol] = swapValue;
c[emptyRow + 1][emptyCol] = empty;
trackEmptySqaure();
}
else if(method == 3){ // up
swapValue = c[emptyRow -1][emptyCol];
c[emptyRow][emptyCol] = swapValue;
c[emptyRow -1][emptyCol] = empty;
trackEmptySqaure();
}
else if(method == 4){// right
swapValue = c[emptyRow][emptyCol + 1];
c[emptyRow][emptyCol] = swapValue;
c[emptyRow ][emptyCol + 1] = empty;
trackEmptySqaure();
}
}
public class DFSSolver {
private ArrayList<Node> closed = new ArrayList<Node>();
private Stack<Node> open = new Stack<Node>();
private PuzzleBoard pb;
private boolean solved;
private int numberOfSteps;
public DFSSolver(PuzzleBoard puzzle) {
pb = puzzle;
numberOfSteps = 0;
solved = false;
Node root = new Node();
root.setState(pb.getCurrentBoard());
addToOpen(root);
checkIfSolved(root);
search();
}
public boolean inOpenList(Node n){
for(Node node: open){
if(node.equals(n)){
return true;
}
}
return false;
}
public boolean inClosedList(Node n){
for(Node node: closed){
if(node.equals(n)){
return true;
}
}
return false;
}
public void addToOpen(Node n){
open.push(n);
}
public void addToClosed(Node n){
closed.add(n);
}
public Node popOpen(){
return open.pop();
}
public void removeFromClosed(Node n){
closed.remove(n);
}
public void search(){
while(!solved){
Node current = popOpen();
if(current != null){
if(!(inClosedList(current))){ // is it previously explored?
checkIfSolved(current);
addChildren(current);
numberOfSteps++;
}
addToClosed(current);
}
}
System.out.println("No of steps: " + numberOfSteps);
}
public void checkIfSolved(Node curr) {
char[][] goal = pb.getGoal();
char[][] current = curr.getState();
for(int i = 0; i < 3; i ++){
for(int j = 0; j < 3; j ++){
char c = current[i][j];
char x = goal[i][j];
if(c != x){
return;
}
}
}
solved = true;
}
public void addChildren(Node parent){
Node newNode = new Node(parent);
newNode = pb.moveLeft(parent);
if(newNode != null){
System.out.println("Parent: " + parent.getState().toString());
System.out.println("atfer moving left");
System.out.println(newNode.toString());
addToOpen(newNode);
}
newNode = pb.moveDown(parent);
if(newNode != null){
System.out.println("Parent: " + parent.getState().toString());
System.out.println("atfer moving down");
System.out.println(newNode.toString());
addToOpen(newNode);
}
newNode = pb.moveRight(parent);
if(newNode != null){
System.out.println("Parent: " + parent.getState().toString());
System.out.println("atfer moving right");
System.out.println(newNode.toString());
addToOpen(newNode);
}
newNode = pb.moveUp(parent);
if(newNode != null){
System.out.println("Parent:\n " + parent.toString());
System.out.println("atfer moving up");
System.out.println(newNode.toString());
addToOpen(newNode);
}
}
【问题讨论】：
-
我找不到你的
swapValues方法... -
@EugenHalca 抱歉，我已经更新了源代码。
-
使用 IDE 中的调试器检查变量的值，您一定会发现错误。