我正在研究骑士的旅行问题，并使用回溯算法。我的代码最终没有产生正确的输出它只是反复重复最后两个条目，直到没有达到n ^ 2 -1。
这是我的代码。我正在关注这个伪代码http://www.wou.edu/~broegb/Cs345/KnightTour.pdf
visited = [[False for x in range(5)] for y in range(5)]
def move(x,y,m):
result=False
if x<0 or x>=5 or y<0 or y>=5:
return False
if visited[x][y]==True:
return False
if m==24:
print "a solution has been found"
print x,",",y
visited[x][y]=True
return True
else:
result=result or move(x+2,y+1,m+1)
result=result or move(x+2,y-1,m+1)
result=result or move(x-2,y+1,m+1)
result=result or move(x-2,y-1,m+1)
result=result or move(x+1,y+1,m+1)
result=result or move(x+1,y-1,m+1)
result=result or move(x-1,y+1,m+1)
result=result or move(x-1,y-1,m+1)
if result==True:
print x,",",y
return True
else:
visited[x][y]=False
return False
答案 0 :(得分：2)
算法结束时，您的设置visited[x][y]=True为true。它必须在你检查那里之后设置。我还为您的代码做了一些改进：
N = 5 # This way you can test it with 5 or 6 and even 100 if you want to.
visited = [[False for x in range(N)] for y in range(N)]
def move(x,y,m):
result=False
if x<0 or x>=N or y<0 or y>=N or visited[x][y]==True: # You may merge these two ifs.
return False
visited[x][y]=True
if m==(N * N - 1):
print "a solution has been found"
visited[x][y]=True # Set visited here tot true.
return True
else:
print x,",",y
if (move(x+2,y+1,m+1) or move(x+2,y-1,m+1)
or move(x-2,y+1,m+1) or move(x-2,y-1,m+1)
or move(x+1,y+1,m+1) or move(x+1,y-1,m+1)
or move(x-1,y+1,m+1) or move(x-1,y-1,m+1)): # Place them in one if.
print x,",",y
return True
return False # If the algorithm comes here it may return false
print move(2,1,0)
答案 1 :(得分：1)
你似乎在下半部分中犯了一个错误。你是在y中加/减1，而这应该是2.完整的一组动作因此如下所示：
result=result or move(x+2,y+1,m+1)
result=result or move(x+2,y-1,m+1)
result=result or move(x-2,y+1,m+1)
result=result or move(x-2,y-1,m+1)
result=result or move(x+1,y+2,m+1)
result=result or move(x+1,y-2,m+1)
result=result or move(x-1,y+2,m+1)
result=result or move(x-1,y-2,m+1)
答案 2 :(得分：1)
您正在实施的伪代码算法存在错误。在递归的情况下，您永远不会将任何visited值设置为True。
在执行任何递归调用之前，请尝试将行visited[x][y]=True从if块移动到以下else块。 （你也可以复制它，但它并没有真正做任何有用的事情。）
答案 3 :(得分：0)
这是Knight在java中的巡演代码，具有出色的布局。我使用递归使用回溯来做到这一点。这是我的班级任务。如果您在理解或运行此代码时遇到任何问题，请与我联系。
package knights.tour;
import java.awt.*;
import java.awt.event.*;
import java.util.logging.*;
import javax.swing.*;
public class KnightsTour extends JFrame implements ActionListener{
//All the static variables used between action listeners and functions.
public static String path;
public static int btnPressed = 0;
public static int rowSelected;
public static String[] pathArray;
public static int[][] coordinatesArray;
public static int columnSelected;
public static int flag =0;
public static int increment = 0;
public static JPanel panel1 = new JPanel();
public static JPanel panel3 ;
public static JButton btnStart = new JButton("Start Animation");
public static JButton btnClear = new JButton("Clear");
public static JTextArea lblPath = new JTextArea();
public static JLabel lblStartRow = new JLabel();
public static JLabel lblStartColumn = new JLabel();
public static JButton[][] button;
public static int variableForIncrement=0;
static int row ;
static int column ;
static int[][] array = new int[row][column];
public static int count = 1;
KnightsTour(){
//Setting layout of the frame in the constructor and adding buttons to the panel and the frame.
getContentPane().setLayout(new GridLayout(2,1));
lblPath.setLineWrap(true);
lblPath.setColumns(10);
lblPath.setSize(700, 100);
lblPath.setEditable(false);
panel1.add(btnStart);
panel1.add(btnClear);
panel1.add(lblStartRow);
panel1.add(lblStartColumn);
panel1.add(lblPath);
panel3 = new JPanel(new GridLayout(row,column));
// Initializing Array of buttons for the user to click on the chess board.
button= new JButton[row][column];
array = new int[row][column];
coordinatesArray = new int[row*column][2]; // This array stores the coordinates as the Knight
for(int i=0;i<row;i++){
for(int j=0;j<column;j++){
button[i][j] = new JButton();
}
}
//Setting background of the buttons to black and white for chessboard layout.
for(int i=0;i<row;i++){
for(int j=0;j<column;j++){
if(i%2 ==j%2){
button[i][j].setBackground(Color.BLACK);
button[i][j].setForeground(Color.WHITE);
}
else{
button[i][j].setBackground(Color.WHITE);
}
panel3.add(button[i][j]);
button[i][j].addActionListener(this);
}
}
btnClear.addActionListener(this);
btnStart.addActionListener(this);
add(panel3);
add(panel1);
setDefaultCloseOperation(EXIT_ON_CLOSE);
}
public static void main(String[] args) {
// TODO code application logic here
String input =JOptionPane.showInputDialog("Enter the rows and columns in the format (row,column)");
String[] ar = input.split(",");
row = Integer.parseInt(ar[0]); // Finding out row and column from the user input.
column = Integer.parseInt(ar[1]);
pathArray = new String[row*column]; // This array is kept to store the path of the knight.
JFrame frame = new KnightsTour();
frame.setVisible(true);
frame.setSize(700,700);
}
//All the computation takes place in this function. It checks the neighbour and recursively calls itself.
public static void neighbourRecursion(int a,int b){
pathArray[increment] = Integer.toString(a) + "," + Integer.toString(b); // Storing the path of the Knight
increment++;
array[a][b] = count; //Stroing value of count.
button[a][b].setText(String.valueOf(count));
coordinatesArray[variableForIncrement][0] = button[a][b].getX(); //Finding coordinates of buttons to show animation
coordinatesArray[variableForIncrement][1] = button[a][b].getY();
count++;
variableForIncrement++;
//Checking for valid neighbours and calling itself recursively.
if(a <= row-3 && b<=column-2){
if(alreadyVisited(a+2,b+1)){
neighbourRecursion(a+2,b+1);
}
}
if(a<=row-3 && b>=1){
if(alreadyVisited(a+2,b-1)){
neighbourRecursion(a+2,b-1);
}
}
if(a>=2 && b<=column-2){
if(alreadyVisited(a-2,b+1)){
neighbourRecursion(a-2,b+1);
}
}
if(a>=2 && b>=1){
if(alreadyVisited(a-2,b-1)){
neighbourRecursion(a-2,b-1);
}
}
if(a<=row-2 && b>=2){
if(alreadyVisited(a+1,b-2)){
neighbourRecursion(a+1,b-2);
}
}
if(a<=row-2 && b<=column-3){
if(alreadyVisited(a+1,b+2)){
neighbourRecursion(a+1,b+2);
}
}
if(a>=1 && b>=2){
if(alreadyVisited(a-1,b-2)){
neighbourRecursion(a-1,b-2);
}
}
if(a>=1 && b <=column-3){
if(alreadyVisited(a-1,b+2)){
neighbourRecursion(a-1,b+2);
}
}
//Breaking condition of the function.
if(count == (row*column)+1){
}
// Backtracking condition if there is no neighbour.
else{
button[a][b].setText("");
array[a][b]=0;
count--;
variableForIncrement--;
if(increment >0){
increment--;
}
return ;
}
}
//This function checks if the neighbour is already visited.
public static boolean alreadyVisited(int a,int b){
if(array[a][b] != 0){
return false;
}
else{
return true;
}
}
@Override
public void actionPerformed(ActionEvent e) {
//when clear is pressed all arrays and global variables are set to initial conditon.
if(e.getSource() == btnClear){
for(int i =0;i<row;i++){
for(int j=0;j<column;j++){
array[i][j] = 0;
button[i][j].setText("");
count = 1;
lblPath.setText("");
lblStartRow.setText("");
lblStartColumn.setText("");
flag =0;
variableForIncrement=0;
increment =0;
path =" ";
}
}
}
//If start animation button is pressed animation is started.
else if(e.getSource() == btnStart){
animate();
}
// When the button is pressed.
else{
for(int i=0;i<row;i++){
for(int j=0;j<column;j++){
if(e.getSource() == button[i][j]){
if(flag == 1){
lblPath.setText(" Please press clear before clicking again"); // Button pressed twice without reset.
}
else{
rowSelected = i;
columnSelected =j;
// If odd * odd board and selected postion is odd then No path is possible.
if(row%2 ==1 && column%2 == 1 && rowSelected%2 ==0 && columnSelected%2 == 1 || row%2 ==1 && column%2 == 1 && rowSelected%2 ==1 && columnSelected%2 == 0){
lblPath.setText(" Path not possible from this point");
}
else{
int count;
lblStartRow.setText("Starting Row : "+String.valueOf(rowSelected + 1));
lblStartColumn.setText("Starting Column : "+String.valueOf(columnSelected + 1));
count = 1;
flag = 1;
startTour(); //Start tour function called.
for(int q=0;q<row;q++){
for(int w=0;w<column;w++){
if(array[i][j] == 0){
count++;
}
}
}
if(count > 2){
lblPath.setText(" No Path found");
}
//Printing path of the knight here.
else{
for(int k=0;k<pathArray.length;k++){
path = path+"->"+ pathArray[k];
}
lblPath.setText(" Path : \n"+ path.substring(5));
}
btnPressed = 1;
break;
}
}
}
}
}
} }
//Function for the animation.
void animate(){
if(btnPressed == 1){
btnPressed =0;
Graphics g = getGraphics();
for(int i=0;i<(row*column)-1;i++){
try {
Thread.sleep(600); // this function slows down drawing of lines.
} catch (InterruptedException ex) {
}
g.setColor(Color.RED); // setting colour or line to red.
g.drawLine((coordinatesArray[i][0]+65),(coordinatesArray[i][1]+50),(coordinatesArray[i+1] [0]+65),(coordinatesArray[i+1][1]+50));
}
}
else{
lblPath.setText(" Please clear, select a button to see the animation again"); //Animate button pressed twice without clear.
}
}
//This function calls the neighbour function with the selected row and column by the user.
static void startTour(){
neighbourRecursion(rowSelected,columnSelected);
for(int i=0;i<row;i++){
for(int j=0;j<column;j++){
System.out.print(array[i][j]+" ");
}
System.out.println();
}
}
}