[LeetCode] Sudoku Solver

Just don't be scared by this problem :-) It's also very standard backtracking problem. This post shares a very concise code, which is rewritten below in C++.

class Solution {
public:
    void solveSudoku(vector<vector<char>>& board) {
        solve(board);
    }
private:
    bool solve(vector<vector<char>>& board) {
        for (int r = 0; r < 9; r++) {
            for (int c = 0; c < 9; c++) {
                if (board[r][c] == '.') {
                    for (char d = '1'; d <= '9'; d++) {
                        if (isValid(board, r, c, d)) {
                            board[r][c] = d;
                            if (solve(board)) return true;
                            board[r][c] = '.';
                        }
                    }
                    return false;
                }
            } 
        }
        return true;
    }
    bool isValid(vector<vector<char>>& board, int r, int c, char d) {
        for (int row = 0; row < 9; row++)
            if (board[row][c] == d) return false;
        for (int col = 0; col < 9; col++)
            if (board[r][col] == d) return false;
        for (int row = (r / 3) * 3; row < (r / 3 + 1) * 3; row++)
            for (int col = (c / 3) * 3; col < (c / 3 + 1) * 3; col++)
                if (board[row][col] == d) return false;
        return true;
    }
};