N Queen Problem

The N Queen, also known as eight queens puzzle, is the problem of placing N chess queens on an N×N chessboard so that no two queens attack each other.

									public const int N = 4;

private static void PrintSolution(int[,] board)
{
	for (int i = 0; i < N; ++i)
	{
		for (int j = 0; j < N; ++j)
			Console.Write(" {0} ", board[i, j]);

		Console.WriteLine();
	}
}

private static bool IsSafe(int[,] board, int row, int col)
{
	int i, j;

	for (i = 0; i < col; ++i)
		if (Convert.ToBoolean(board[row, i]))
			return false;

	for (i = row, j = col; i >= 0 && j >= 0; --i, --j)
		if (Convert.ToBoolean(board[i, j]))
			return false;

	for (i = row, j = col; j >= 0 && i < N; ++i, --j)
		if (Convert.ToBoolean(board[i, j]))
			return false;

	return true;
}

private static bool SolveNQ(int[,] board, int col)
{
	if (col >= N)
		return true;

	for (int i = 0; i < N; ++i)
	{
		if (IsSafe(board, i, col))
		{
			board[i, col] = 1;

			if (SolveNQ(board, col + 1))
				return true;

			board[i, col] = 0;
		}
	}

	return false;
}

public static bool Solve()
{
	int[,] board = {
		{ 0, 0, 0, 0 },
		{ 0, 0, 0, 0 },
		{ 0, 0, 0, 0 },
		{ 0, 0, 0, 0 }
	};

	if (SolveNQ(board, 0) == false)
		return false;

	PrintSolution(board);
	return true;
}

Example

									bool isSolved = Solve();

Output

									isSolved: true

Output of Solve function:
 0  0  1  0
 1  0  0  0
 0  0  0  1
 0  1  0  0