board.java

The famous 8-queen problem in java

package queenProblem;

public class Board {
	
	private int queens[];
	private int count;
	
	public Board() {
		queens = new int[8];
		count = 0;
	}

	public int[] getQueens() {
		return queens;
	}

	public void setQueens(int[] queens) {
		this.queens = queens;
	}

	public void putQueens() {
		putQueen(0);
	}
	
	private void putQueen(int numberOfQueen) {
		if(numberOfQueen < 8) {
			for(int column = 0; column < 8; column++) {
				if(isValid(numberOfQueen, column)) {
					queens[numberOfQueen] = column;
					putQueen(numberOfQueen + 1);
				}
			}
		}
		
		else {
			System.out.println("------- " + (count+1) + " ---------");
			printQueens();
			count++;
			System.out.println();
		}
	}
	
	private boolean isValid(int row, int column) {
		for(int i = 0; i < row; i++) {
			if(queens[i] == column)
				return false;
			
			if(Math.pow(queens[i] - column, 2) == Math.pow(i - row, 2)) 
				return false;
		}
		
		return true;
	}
	
	public void printQueens() {
		for(int i = 0; i < queens.length; i++) { 
			for(int j = 0; j < 8; j++) {
				if(queens[i] == j)
					System.out.print('q' + " ");
				
				else
					System.out.print('*' + " ");
			}
			System.out.println();
		}
	}
}