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BACKTRACKING4.java
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BACKTRACKING4.java
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public class BACKTRACKING4 {
public static void printBoard(char board[][]) {
System.out.println("<------ CHESS BOARD ------>");
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
System.out.print(board[i][j] + " ");
}
System.out.println();
}
System.out.println();
}
public static boolean isSafe(char board[][], int i, int j) {
// CHECKS WHETHER IT'S SAFE TO PUT QUEEN IN THAT CELL ?
// VERTICAL UP?
for (int k = i - 1; k >= 0; k--) {
if (board[k][j] == 'Q') {
return false;
}
}
// DIAGONAL LEFT UP?
for (int p = i - 1, q = j - 1; p >= 0 && q >= 0; p--, q--) {
if (board[p][q] == 'Q') {
return false;
}
}
// DIAGONAL RIGHT UP??
for (int p = i - 1, q = j + 1; p >= 0 && q <= board.length - 1; p--, q++) {
if (board[p][q] == 'Q') {
return false;
}
}
return true;
}
public static void QueenWays(char board[][], int i) {
if (i == board.length) {
printBoard(board);
return;
}
for (int j = 0; j < board.length; j++) {
if (isSafe(board, i, j)) {
board[i][j] = 'Q';
QueenWays(board, i + 1);
board[i][j] = 'x';
}
}
}
public static void main(String[] args) {
// PLACE N QUEENS ON A (N X N) CHESSBOARD SUCH THAT NO 2 QUEENS ATTACK EACH OTHER
int n = 4;
char board[][] = new char[n][n];
for (int i = 0; i < board.length; i++) {
for (int j = 0; j < board[0].length; j++) {
board[i][j] = 'x';
}
}
QueenWays(board, 0);
}
}