import java.util.*;

public class SudokuSolver {

	public String solve(Board B){

		Stack<Move> stackOfMoves = new Stack<Move>();

		try{

			int row = 0;
			int col = 0;
			int guess = 1;
			boolean badMove = true;

			while(badMove==true && row<9){
				if(B.getFixedCell(row,col)==false)
				{
					//Check if the move is bad
					Move m = new Move(row,col,guess);
					badMove = B.isBad(m);

					if(badMove==false)
					{
						B.move(m);
						stackOfMoves.push(m);

						//Move to next cell
						if(col!=8)
							col++;
						else{
							row++;
							col =0;
						}

						guess = 1;
						badMove=true;
					}
					else
					{
						//If there are more guesses, increment guess
						if(guess!=9)
							guess++;
						else
						{
							//go back and try the next guess for the top Move on stack
							Move m_last = stackOfMoves.pop();

							row = m_last.getRow();
							col = m_last.getCol();	

							Move tmp = new Move(row,col, 0);
							B.move(tmp);

							//If the top Move guess is '9', skip it
							while(m_last.getValue()==9)
							{
								m_last = stackOfMoves.pop();
								row = m_last.getRow();
								col = m_last.getCol();

								Move tmp2 = new Move(row,col,0);
								B.move(tmp2);
							}

							//increment guess
							guess = m_last.getValue()+1;

						}
					}
				}
				else
				{
					//Move to next cell
					if(col!=8)
						col++;
					else{
						row++;
						col =0;
					}
				}
			}		

		}catch(EmptyStackException e){
			return "This puzzle has no solution.";
		};

		return B.toString();
	}

}