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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;
    }
};


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