[Leetcode] Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

没啥算法，纯模拟！

class Solution {
public:
    bool isValidCell(vector<vector<char> > &board, int a, int b) {
        vector<bool> flag(9, false);
        int idx;
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                idx = board[a + i][b + j] - '0';
                if (idx > 0 && idx <= 9 && !flag[idx])  
                    flag[idx] = true;
                else if (idx > 0 && idx <= 9 && flag[idx])
                    return false;
            }
        }
        return true;
    }
    
    bool isValidRow(vector<vector<char> > &board, int a) {
        vector<bool> flag(9, false);
        int idx;
        for (int j = 0; j < 9; ++j) {
            idx = board[a][j] - '0';
            if (idx > 0 && idx <= 9 && !flag[idx])  
                flag[idx] = true;
            else if (idx > 0 && idx <= 9 && flag[idx])
                return false;
        }
        return true;
    }
    
     bool isValidCol(vector<vector<char> > &board, int b) {
        vector<bool> flag(9, false);
        int idx;
        for (int i = 0; i < 9; ++i) {
            idx = board[i][b] - '0';
            if (idx > 0 && idx <= 9 && !flag[idx])  
                flag[idx] = true;
            else if (idx > 0 && idx <= 9 && flag[idx])
                return false;
        }
        return true;
    }
    
    bool isValidSudoku(vector<vector<char> > &board) {
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                if (!isValidCell(board, 3 * i, 3 * j)) 
                    return false;
            }
        }
        for (int i = 0; i < 9; ++i) {
            if (!isValidRow(board, i))
                return false;
        }
        for (int j = 0; j < 9; ++j) {
            if (!isValidCol(board, j))
                return false;
        }
        return true;
    }
};