/* Java program to solve N Queen Problem using
backtracking */
public class NQueenProblem
{
	final int N = 4;

	/* A utility function to print solution */
	void printSolution(int board[][])
	{
		for (int i = 0; i < N; i++)
		{
			for (int j = 0; j < N; j++)
				System.out.print(" " + board[i][j]
								+ " ");
			System.out.println();
		}
	}

	/* A utility function to check if a queen can
	be placed on board[row][col]. Note that this
	function is called when "col" queens are already
	placeed in columns from 0 to col -1. So we need
	to check only left side for attacking queens */
	boolean isSafe(int board[][], int row, int col)
	{
		int i, j;

		/* Check this row on left side */
		for (i = 0; i < col; i++)
			if (board[row][i] == 1)
				return false;

		/* Check upper diagonal on left side */
		for (i=row, j=col; i>=0 && j>=0; i--, j--)
			if (board[i][j] == 1)
				return false;

		/* Check lower diagonal on left side */
		for (i=row, j=col; j>=0 && i<N; i++, j--)
			if (board[i][j] == 1)
				return false;

		return true;
	}

	/* A recursive utility function to solve N
	Queen problem */
	boolean solveNQUtil(int board[][], int col)
	{
		/* base case: If all queens are placed
		then return true */
		if (col >= N)
			return true;

		/* Consider this column and try placing
		this queen in all rows one by one */
		for (int i = 0; i < N; i++)
		{
			/* Check if queen can be placed on
			board[i][col] */
			if (isSafe(board, i, col))
			{
				/* Place this queen in board[i][col] */
				board[i][col] = 1;

				/* recur to place rest of the queens */
				if (solveNQUtil(board, col + 1) == true)
					return true;

				/* If placing queen in board[i][col]
				doesn't lead to a solution then
				remove queen from board[i][col] */
				board[i][col] = 0; // BACKTRACK
			}
		}

		/* If queen can not be place in any row in
		this colum col, then return false */
		return false;
	}

	/* This function solves the N Queen problem using
	Backtracking. It mainly uses solveNQUtil() to
	solve the problem. It returns false if queens
	cannot be placed, otherwise return true and
	prints placement of queens in the form of 1s.
	Please note that there may be more than one
	solutions, this function prints one of the
	feasible solutions.*/
	boolean solveNQ()
	{
		int board[][] = {{0, 0, 0, 0},
			{0, 0, 0, 0},
			{0, 0, 0, 0},
			{0, 0, 0, 0}
		};

		if (solveNQUtil(board, 0) == false)
		{
			System.out.print("Solution does not exist");
			return false;
		}

		printSolution(board);
		return true;
	}

	// driver program to test above function
	public static void main(String args[])
	{
		NQueenProblem Queen = new NQueenProblem();
		Queen.solveNQ();
	}
}
