#include "sudoku.h"

Sudoku::Sudoku()
{
}

void Sudoku::set_value(int row, int column, int value)
{
	sudoku_cell[row][column].set_value(value);
}

int Sudoku::solve_step(int pos_row, int pos_column)
{
	// verify if the cell has already been solved
	if ((value(pos_row,pos_column) > 0 ) && (value(pos_row,pos_column) <= 9)) {
		return value(pos_row,pos_column);
	}
	
	bool possible_solution[9];
	
	for (int idx = 0; idx < 9; idx++) {
		possible_solution[idx] = true; 
	}
	
	// eliminate row
	for (int column = 0; column < 9; column++) {
		if (column != pos_column) {
			const int v = value(pos_row,column);
			if ((v > 0) && (v <= 9)) {
				possible_solution[v - 1] = false;
			}
		}
	}
	// eliminate column
	for (int row = 0; row < 9; row++) {
		if (row != pos_row) {
			const int v = value(row,pos_column);
			if ((v > 0) && (v <= 9)) {
				possible_solution[v - 1] = false;
			}
		}
		
	}
	
	// eliminate subgrid
	int grid_row = pos_row - (pos_row % 3);
	int grid_column = pos_column - (pos_column % 3);
	for (int row = grid_row; row < grid_row + 3; row++) {
		for (int column = grid_column; column < grid_column + 3; column ++) {
			if ((column != pos_column) && (row != pos_row)) {
				const int v = value(row, column);
				if ((v > 0) && (v <= 9)) {
					possible_solution[v - 1] = false;
				}	
			}
			
		}
		
	}
	
	int nbeliminated = 0;
	int solution = 0;
	for (int idx = 0; idx < 9; idx++) {
		if (!possible_solution[idx]) {
			nbeliminated++;
		} else {
			solution = idx + 1;
		}
	}
	
	if (nbeliminated == 8) {
		return solution;
	} else {
		return 0;
	}
}