Question: java: The last column doesn't print a Queen. Most of it is source code and the error is from the displayBoard method. What am I
java: The last column doesn't print a Queen. Most of it is source code and the error is from the displayBoard method. What am I doing wrong?
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) {
// --------------------------------------------------
// Set a queen at square indicated by row and
// column.
// Precondition: None.
// Postcondition: Sets the square on the board in a
// given row and column to QUEEN.
// --------------------------------------------------
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 if (board[i][column-1]==1){ return true; } } // check row for (int i=0; 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 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
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