QueensProblem.java

public class QueensProblem {
	private static int boardSize = 8; // default board size is 8x8
	private static int[] board = new int[boardSize];
	private static StringBuilder output;

	public static void main(String[] args) {
		if(args != null && args.length > 0) {
			try {
				boardSize = Integer.parseInt(args[0]);
				board = new int[boardSize];
			} catch(NumberFormatException ex) {
				System.out.println("Invalide board size provided.");
			}
		}

		if(boardSize < 4 || boardSize > 25) {
			System.out.println("Board size is out the permissible value of 4 and 25 (both inclusive)");
			System.exit(1);
		}

		output = new StringBuilder();
		placeAllQueens(board, 0);
	}

	private static void placeAllQueens(int board[], int row){
  		if(row == board.length) {
   			prepareBoard(board);
   			output.deleteCharAt(output.length() - 1);

			System.out.println("Queens on: " + output.toString());

			System.exit(1);
  		} else {
   			for (int col = 0; col < board.length; col++) {
    			board[row] = col;
    			if(isPlacingSafe(board, row)){
     				placeAllQueens(board, row+1);
    			}
   			}
  		}
 	}

 	private static boolean isPlacingSafe(int[] board, int currentRow) {
  		for (int previousRows = 0; previousRows < currentRow; previousRows++) {
 
	   		//Same Column Checking
	   		if(board[currentRow] == board[previousRows]) {
	    		return false;
	   		}
	 
	   		//Minor Diagonal Checking
	   		if( (board[currentRow] - board[previousRows]) == currentRow - previousRows) {
	    		return false;
	   		}
	 
	   		//Major Diagonal Checking
	   		if( (board[previousRows] - board[currentRow]) == currentRow - previousRows) {
	    		return false;
	   		}
	 
	   		//Major and Minor Diagonal Checking
			if (Math.abs(board[currentRow] - board[previousRows]) == Math.abs(currentRow - previousRows)) {
	    		return false;
	   		}
	  	}

	  	return true;
 	}
 
 	private static void prepareBoard(int[] board){
  		for (int row = 0; row < board.length; row++) {
   			for (int col = 0; col < board.length; col++) {
    			if(board[row] == col){
     				output.append("(" + (row + 1) + "," + (col + 1) + "),");
			    }
   			}
  		}
	 }
}