suduko_solver.cpp

/*Write a program to solve a Sudoku puzzle by filling the empty cells.

A sudoku solution must satisfy all of the following rules:

Each of the digits 1-9 must occur exactly once in each row.
Each of the digits 1-9 must occur exactly once in each column.
Each of the digits 1-9 must occur exactly once in each of the 9 3x3 sub-boxes of the grid.
The '.' character indicates empty cells.*/
class Solution {
public:
    bool isValid(vector<vector<char>>& board,int row,int col,char ch)
    {
        for(int i=0;i<9;i++)
        {
            if(board[i][col]==ch)
                            return false;
            
            if(board[row][i]==ch)
                            return false;
            
            if(board[3*(row/3)+i/3][3*(col/3)+i%3]==ch)
                return false;             
        }
        return true;
    }
    bool solve(vector < vector < char >> & board) {
        for (int i = 0; i < board.size(); i++) {
            for (int j = 0; j < board[0].size(); j++) {
                if (board[i][j] == '.') {
                    for (char c = '1'; c <= '9'; c++) {
                        if (isValid(board, i, j, c)) {
                            board[i][j] = c;

                            if (solve(board))
                                 return true;
                            else
                                board[i][j] = '.';
                        }
                    }

        return false;
      }
    }
  }
  return true;
}
    
    void solveSudoku(vector<vector<char>>& board) {
        solve(board);
    }
    
    
};