main.cpp

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const int SIZE = 9;

bool isSafe(const vector<vector<int>>& board, int row, int col, int num) {
    for (int x = 0; x < SIZE; x++) {
        if (board[row][x] == num || board[x][col] == num ||
            board[row - row % 3 + x / 3][col - col % 3 + x % 3] == num) {
            return false;
        }
    }
    return true;
}

bool solveSudoku(vector<vector<int>>& board) {
    for (int row = 0; row < SIZE; row++) {
        for (int col = 0; col < SIZE; col++) {
            if (board[row][col] == 0) {
                for (int num = 1; num <= SIZE; num++) {
                    if (isSafe(board, row, col, num)) {
                        board[row][col] = num;
                        if (solveSudoku(board)) {
                            return true;
                        }
                        board[row][col] = 0;
                    }
                }
                return false;
            }
        }
    }
    return true;
}

void printBoard(const vector<vector<int>>& board) {
    for (const auto& row : board) {
        for (int num : row) {
            cout << num << " ";
        }
        cout << endl;
    }
}

int main() {
    vector<vector<int>> board = {
        {5, 3, 0, 0, 7, 0, 0, 0, 0},
        {6, 0, 0, 1, 9, 5, 0, 0, 0},
        {0, 9, 8, 0, 0, 0, 0, 6, 0},
        {8, 0, 0, 0, 6, 0, 0, 0, 3},
        {4, 0, 0, 8, 0, 3, 0, 0, 1},
        {7, 0, 0, 0, 2, 0, 0, 0, 6},
        {0, 6, 0, 0, 0, 0, 2, 8, 0},
        {0, 0, 0, 4, 1, 9, 0, 0, 5},
        {0, 0, 0, 0, 8, 0, 0, 7, 9}
    };

    if (solveSudoku(board)) {
        printBoard(board);
    } else {
        cout << "No solution exists" << endl;
    }

    return 0;
}