36. Valid Sudoku

---

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

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

A partially filled sudoku which is valid.

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

Example 1:

Input:
[
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
Output: true

Example 2:

Input:
[
  ["8","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being 
    modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.
• The given board contain only digits 1-9 and the character '.'.
• The given board size is always 9x9.

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) 
    {
        for(int i = 0;i<9;i++)//rows
        { 
            set<char> myset;
            for(int j = 0;j<9;j++){
                if(board[i][j] == '.') continue;
                if(myset.find(board[i][j])==myset.end())
                    myset.insert(board[i][j]);
            else
                return false;
            }
        }
        
        for(int i = 0;i<9;i++)//cols
        { 
            set<char> myset;
            for(int j = 0;j<9;j++){
                if(board[j][i] == '.') continue;
                if(myset.find(board[j][i])==myset.end())
                    myset.insert(board[j][i]);
            else
                return false;
            }
        }    
        
        for(int sub_i = 0;sub_i < 3;sub_i++)//sub-box
            for(int sub_j = 0 ;sub_j < 3; sub_j++)
            { 
                set<char> myset;
                for(int i = 0;i<3;i++)
                    for(int j =0;j<3;j++)
                    {
                    
                    if(board[sub_i*3+i][sub_j*3+j] == '.') continue;
                    if(myset.find(board[sub_i*3+i][sub_j*3+j])==myset.end())
                        myset.insert(board[sub_i*3+i][sub_j*3+j]);
                    else
                        return false;
                    }
            }
               
        return true;   
        
    }
   
};