Sudoku Solver

Sudoku Solver

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

A sudoku solution must satisfy all of the following rules:

1. Each of the digits 1-9 must occur exactly once in each row.
2. Each of the digits 1-9 must occur exactly once in each column.
3. 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.

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: [["5","3","4","6","7","8","9","1","2"],["6","7","2","1","9","5","3","4","8"],["1","9","8","3","4","2","5","6","7"],["8","5","9","7","6","1","4","2","3"],["4","2","6","8","5","3","7","9","1"],["7","1","3","9","2","4","8","5","6"],["9","6","1","5","3","7","2","8","4"],["2","8","7","4","1","9","6","3","5"],["3","4","5","2","8","6","1","7","9"]]
Explanation: The input board is shown above and the only valid solution is shown below:

Constraints:

• board.length == 9
• board[i].length == 9
• board[i][j] is a digit or '.'.
• It is guaranteed that the input board has only one solution.

Solution To the Above Question

class Solution {

public:

    //For checking if the input is Valid or not

    bool isValid(vector<vector<char>>& board, int row, int col, char c){

        int RowNum=(row/3)*3;

        int ColNum=(col/3)*3;

        

        for(int i=0; i<9; i++){

            if((board[i][col]==c) || (board[row][i]==c) || (board[RowNum+i/3][ColNum+i%3]==c)) {

                return false;

            }

        }

        return true;

    } 

    // For Solving the Sudoku 

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

        for(int i=0; i<9; i++){

            for(int j=0; j<9; 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;

    } 

    //Main Function

    void solveSudoku(vector<vector<char>>& board) {

         solve(board);

    }

};