NQueen3.java

public class NQueen3 {
    public static boolean isSafe(char board[][], int row, int col){
        for(int i = row-1;i>= 0;i--){
            if(board[i][col] == 'Q'){
                return false;
            }
        }

        for(int i = row-1, j = col-1 ; i>=0 && j >= 0 ; i--, j--){
            if(board[i][j] == 'Q'){
                return false;
            }
        }

        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 boolean nQueen(char board[][], int row){
        if(row == board.length){
            // printBoard(board);
            return true;
        }

        for(int j = 0;j<board.length; j++){
            if(isSafe(board, row, j)){
                board[row][j] = 'Q';
                if(nQueen(board, row+1)){
                    return true;
                }
                board[row][j] = 'x';
            }
        }
        return false;
    }
    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 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';
            }
        }

        if(nQueen(board, 0)){
            System.out.println("Solution exists");
            printBoard(board);
        }else{
            System.out.println("solution doesn't exist");
        }
    }
}