A simple implementation of the 8 queens problem - recursive backtracking.

EightQueens.java

import java.awt.Point;

public class EightQueens {

	/**
	 * @param args
	 */
	public static void main(String[] args) {

		boolean board[][] = new boolean[8][8];

		recBoard(board, 0);
	}

	public static void recBoard(boolean board[][], int p) {
		if (p == 8) {
			System.out.println("Found one possible config");
			printBoard(board);
			return;
		} else {
			for (int i = 0; i < board.length; i++) {
				board[p][i] = true;
				if (isBoardValid(board)) {
					recBoard(board, p + 1);
				}
				board[p][i] = false;
			}
		}
	}

	public static void printBoard(boolean board[][]) {
		for (int i = 0; i < board.length; i++) {
			for (int j = 0; j < board.length; j++) {
				if (board[i][j])
					System.out.print(" Q ");
				else
					System.out.print(" - ");
			}
			System.out.println();
		}
	}

	public static boolean isBoardValid(boolean board[][]) {
		boolean isValid = true;
		Point curr = new Point();
		for (int i = 0; i < board.length; i++) {
			for (int j = 0; j < board.length; j++) {
				if (board[i][j]) {
					curr.x = i;
					curr.y = j;
					// check left to right
					for (int j1 = 0; j1 < board.length; j1++) {
						if (board[curr.x][j1] && j1 != curr.y) {
							isValid = false;
						}
					}
					// check up to down
					for (int i1 = 0; i1 < board.length; i1++) {
						if (board[i1][curr.y] && i1 != curr.x) {
							isValid = false;
						}
					}
					// check diagonals
					int i1 = curr.x;
					int j1 = curr.y;
					while (i1 > 0 && j1 > 0) {
						i1--;
						j1--;
						if (board[i1][j1])
							isValid = false;
					}
					i1 = curr.x;
					j1 = curr.y;
					while (i1 < board.length - 1 && j1 < board.length - 1) {
						i1++;
						j1++;
						if (board[i1][j1])
							isValid = false;
					}
					i1 = curr.x;
					j1 = curr.y;
					while (i1 > 0 && j1 < board.length - 1) {
						i1--;
						j1++;
						if (board[i1][j1])
							isValid = false;
					}
					i1 = curr.x;
					j1 = curr.y;
					while (i1 < board.length - 1 && j1 > 0) {
						i1++;
						j1--;
						if (board[i1][j1])
							isValid = false;
					}
				}
			}
			if (!isValid)
				break;
		}
		return isValid;
	}
}

The recBoard is the main recursive function. Just 15 lines does it. Impressive. But the reason the code is this huge is because I couldnt find a better way to validate the board for diagonals in a simpler manner. (Literally ugly code for that part).