SudokuSolver.cpp

class Solution {
    bool check(vector<vector<char>> &board, int i, int j, char val)
    {
        int row = i - i % 3, column = j - j % 3;
        for (int x = 0; x < 9; x++) if (board[x][j] == val) return false;
        for (int y = 0; y < 9; y++) if (board[i][y] == val) return false;
        for (int x = 0; x < 3; x++)
            for (int y = 0; y < 3; y++)
                if (board[row + x][column + y] == val) return false;
        return true;
    }
    bool solveSudoku(vector<vector<char>> &board, int i, int j)
    {
        if (i == 9) return true;
        if (j == 9) return solveSudoku(board, i + 1, 0);
        if (board[i][j] != '.') return solveSudoku(board, i, j + 1);

        for (char c = '1'; c <= '9'; c++)
        {
            if (check(board, i, j, c))
            {
                board[i][j] = c;
                if (solveSudoku(board, i, j + 1)) return true;
                board[i][j] = '.';
            }
        }

        return false;
    }
public:
    void solveSudoku(vector<vector>& board) {
        solveSudoku(board, 0, 0);
    }
}