我在这里看到了与此类似的帖子,但是我的帖子略有不同。
我编写了displayBoard方法,但最后一列未返回Queen。
是因为女王的值是1并抛弃了数字吗?
它一直告诉我我有一个ArrayOutOfBoundsException: -1
我知道数组的计数为0,但仍然无法正常工作
public class Queens
{
public static final int BOARD_SIZE = 8;
public static final int EMPTY = 0;
public static final int QUEEN = 1;
private int board[][];
public Queens()
{
board = new int[BOARD_SIZE][BOARD_SIZE];
}
public void clearBoard()
{
board = new int[BOARD_SIZE][BOARD_SIZE];
}
public void displayBoard () {
int counter = 0;
for (int i = 0; i < BOARD_SIZE; i++)
{
for (int j = 0 ; j < BOARD_SIZE; j++)
{
if (board[i][j] == QUEEN )
{
System.out.print("| X |");
counter++;
}
else
{
System.out.print("| 0 |");
}
}
System.out.println();
}
}
public boolean placeQueens(int column) {
if (column >= BOARD_SIZE) {
return true; // base case
}
else {
boolean queenPlaced = false;
int row = 1; // number of square in column
while ( !queenPlaced && (row <= BOARD_SIZE) ) {
// if square can be attacked
if (isUnderAttack(row, column)) {
++row; // consider next square in column
} // end if
else { // place queen and consider next column
setQueen(row, column);
queenPlaced = placeQueens(column+1);
// if no queen is possible in the next column,
if (!queenPlaced) {
// backtrack: remove queen placed earliers
// and try next square in column
removeQueen(row, column);
++row;
} // end if
} // end if
} // end while
return queenPlaced;
} // end if
} // end placeQueens
private void setQueen(int row, int column) {
board[row-1][column-1] = QUEEN;
} // end setQueen
private void removeQueen(int row, int column) {
board[row-1][column-1] = EMPTY;
} // end setQueen
private boolean isUnderAttack(int row, int column) {
// check column
for (int i=0; i<row-1; i++){
if (board[i][column-1]==1){
return true;
}
}
// check row
for (int i=0; i<column-1; i++) {
if (board[row-1][i] == 1){
return true;
}
}
// check lower diagnal
int lower_dir_row = row-2;
int lower_dir_column = column-2;
while (lower_dir_row>=0 && lower_dir_column>=0){
if (board[lower_dir_row][lower_dir_column]==1){
return true;
} else {
lower_dir_row = lower_dir_row -1;
lower_dir_column = lower_dir_column -1;
}
}
// check upper diagnal
int upper_dir_row = row;
int upper_dir_column = column-2;
while (upper_dir_row<BOARD_SIZE && upper_dir_column>=0){
if(board[upper_dir_row][upper_dir_column] ==1){
return true;
}else{
upper_dir_row = upper_dir_row +1;
upper_dir_column = upper_dir_column -1;
}
}
return false;
} // end isUnderAttack
public static void main(String[] s)
{
Queens q = new Queens();
q.placeQueens(0);
q.displayBoard();
}
} // end Queens
最佳答案
您需要在placeQueens()方法中更改while循环
while ( !queenPlaced && (row <= BOARD_SIZE) ) {...}
while循环应为
while ( !queenPlaced && (row < BOARD_SIZE) ) {...}
此外,在setQueen(...)和removeQueen(...)函数中,您从不进行边界检查,并假定可以使用传入的参数访问电路板。您需要确保两个值都小于BOARD_SIZE,然后再设置或删除板阵列中的皇后区。
private void setQueen(int row, int column) {
if(row - 1 < BOARD_SIZE && column - 1 < BOARD_SIZE)
board[row-1][column-1] = QUEEN;
} // end setQueen
private void removeQueen(int row, int column) {
if(row - 1 < BOARD_SIZE && column - 1 < BOARD_SIZE)
board[row-1][column-1] = EMPTY;
} // end setQueen
最后,由于您要自己施加1的费用,因此应将主电话改为(Credit @Ian Mc)
q.placeQueens(1);
但是,如果要简化程序,则不应应用偏移量,因为这通常会引入用户错误。这是使程序无偏移运行的方法
(1)在您的isUnderAttack方法内添加检查,以确保您在访问有效的行和列之前先检查一下有效的行和列,并进行简单的检查(仅检查0和更大的值)
private boolean isUnderAttack(int row, int column) {
// check column
for (int i=0; i<row-1; i++){
/* add a check to ensure the column offset index is valid */
if (column - 1 >= 0 && board[i][column-1]==1){
return true;
}
}
// check row
for (int i=0; i<column-1; i++) {
/* add a check to ensure the row offset index is valid */
if (row - 1 >= 0 && board[row-1][i] == 1){
return true;
}
}
(2)然后从remove和set Queen方法中删除偏移量
private void setQueen(int row, int column) {
if(row < BOARD_SIZE && column < BOARD_SIZE)
board[row][column] = QUEEN;
} // end setQueen
private void removeQueen(int row, int column) {
if(row < BOARD_SIZE && column < BOARD_SIZE)
board[row][column] = EMPTY;
} // end setQueen
(3)确保从0到BOARD_SIZE-1个内部placeQueens(...)方法循环
while ( !queenPlaced && (row < BOARD_SIZE) ) {
(4)最后从索引0开始
q.placeQueens(0);
输出量
| 0 || 0 || 0 || 0 || 0 || 0 || 0 || 0 |
| 0 || 0 || 0 || 0 || 0 || 0 || X || X |
| 0 || 0 || 0 || 0 || 0 || X || 0 || 0 |
| 0 || 0 || 0 || 0 || X || 0 || 0 || 0 |
| 0 || 0 || 0 || X || 0 || 0 || 0 || 0 |
| 0 || 0 || X || 0 || 0 || 0 || 0 || 0 |
| 0 || X || 0 || 0 || 0 || 0 || 0 || 0 |
| X || 0 || 0 || 0 || 0 || 0 || 0 || 0 |