Valid Sudoku

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Each row must contain the digits 1-9 without repetition.
Each column must contain the digits 1-9 without repetition.
Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

此题要求判断一个数独是否有效？
规则：
同一行，同一列，同一个33小方块都只含1-9中的不重复数字。解法也按照规则来，判断同行同列同33小方块内是否有重复数字，若无则ok，否则不行。

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        set<string> s;
        string s1="in row";
        string s2="in col";
        string s3="in square";
        for (int i=0;i<board.size();i++)
        {
            for (int j=0;j<board[0].size();j++)
            {
                char ch=board[i][j];
                if(ch!='.')
                {
                    cout<<ch<<endl;
                    string row=ch+s1+to_string(i),col=ch+s2+to_string(j),square=ch+s3+to_string(i/3)+to_string(j/3);
                    //cout<<row<<col<<square<<endl;
                    if(s.count(row)||s.count(col)||s.count(square))
                    {
                        return false;
                    }
                    else
                    {
                        s.insert(row);
                        s.insert(col);
                        s.insert(square);
                    }
                }
            }
        }
        return true;
    }
};