leetcode 36 solution

 36. Valid Sudoku

Determine if a 9 x 9 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 nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

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.

 

Example 1:

Input: board = 
[["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: board = 
[["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.

 

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit 1-9 or '.'.

solution:

class Solution {

public:

    bool isValidSudoku(vector<vector<char>>& board) {

        

        unordered_set<string>map;

        

        for(int i = 0; i <9 ; i++  )

        {

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

            {   

                int box = (i/3)*3 + (j/3);

                if(board[i][j] != '.')

                {   

                     string s = "row";

                     string t = "col";

                      string u = "box";

                    char a = i+'0';

                    char b = j +'0';

                        char c = box +'0';

                    s = s+a+ board[i][j];

                    t = t+b+ board[i][j];

                    u = u+c+ board[i][j];

                    if(map.find(s) == map.end())

                    map.insert(s);

                    else

                     return false;

                    if(map.find(t) == map.end())

                    map.insert(t);

                    else

                     return false;

                    if(map.find(u) == map.end())

                    map.insert(u);

                    else

                     return false;

                    

                }

            }

            

        }

        

        return true;

    }

};