NQueen1.java

public class NQueen1 {
    public static void printBoard(char board[][]){
        for(int i = 0;i<board.length ;i++){
            for(int j = 0;j<board.length ;j++){
                System.out.print(board[i][j] + " ");
            }
            System.out.println();
        }
    }
    public static boolean isSafe(char board[][], int row, int col){
        //vertically up
        for(int i = row-1; i>=0;i--){
            if(board[i][col] == 'Q'){
                return false;
            }
        }
        //primary diagonal
        for(int i = row-1, j= col-1 ;i >= 0 && j >= 0 ;i--,j--){
            if(board[i][j] == 'Q'){
                return false;
            }
        }
        //secondary diagonal
        for(int i = row-1, j = col+1 ; i>=0 && j<board.length ;i--,j++){
            if(board[i][j] == 'Q'){
                return false;
            }
        }
        return true;
    }
    public static int count = 0;
    public static void nQueen(char board[][], int row){
        if(row == board.length){
            // printBoard(board);
            count++;
            // System.out.println();
            return;
        }

        for(int j = 0;j<board.length ;j++){
            if(isSafe(board, row, j)){
                board[row][j] = 'Q';
                nQueen(board, row+1);
                board[row][j] = 'x';
            }
        }
    }
    
    public static void main(String args[]){
        int n = 4;
        char board[][] = new char[n][n];

        for(int i =0;i<board.length ;i++){
            for(int j =0 ;j<board.length;j++){
                board[i][j] = 'x';
            }
        }
        nQueen(board,0);
        System.out.println(count);
    }
}