Sudoku_Solver.cpp

#include <iostream>
#include <vector>

using namespace std;

const int N = 9;

bool isValid(vector<vector<char>>& board, int row, int col, char num) {
    for (int i = 0; i < N; i++) {
        if (board[row][i] == num || board[i][col] == num || board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == num)
            return false;
    }
    return true;
}

bool solveSudoku(vector<vector<char>>& board) {
    for (int row = 0; row < N; row++) {
        for (int col = 0; col < N; col++) {
            if (board[row][col] == '.') {
                for (char num = '1'; num <= '9'; num++) {
                    if (isValid(board, row, col, num)) {
                        board[row][col] = num;
                        if (solveSudoku(board))
                            return true;
                        board[row][col] = '.'; // Backtrack
                    }
                }
                return false;
            }
        }
    }
    return true;
}

int main() {
    vector<vector<char>> board(N, vector<char>(N));
    // Input the Sudoku board here
    // '.' represents empty cells

    for (int i = 0; i < N; i++) {
        for (int j = 0; j < N; j++) {
            cin >> board[i][j];
        }
    }

    if (solveSudoku(board)) {
        for (int i = 0; i < N; i++) {
            for (int j = 0; j < N; j++) {
                cout << board[i][j] << " ";
            }
            cout << endl;
        }
    } else {
        cout << "No solution exists." << endl;
    }

    return 0;
}