/**
knaul853

//https://stackoverflow.com/a/10163885/9959901
**/
class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {

        unordered_set<char> row[9],col[9],square[3][3];

        for(int i=0;i<9;i++){
            for(int j=0;j<9;j++){

                char ch = board[i][j];

                if(ch !='.'){

                    if(!row[i].insert(ch).second || !col[j].insert(ch).second
                                       || !square[i/3][j/3].insert(ch).second) return false;
                }
            }
        }

        return true;
    }
};