Solves a Sudoku puzzle < C++>

#include <iostream>
#include <vector>
using namespace std;

bool isSafe(vector<vector<int>>& grid, int row, int col, int num) {
    // Check if the number is already present in the current row or column
    for (int i = 0; i < 9; ++i) {
        if (grid[row][i] == num || grid[i][col] == num) {
            return false;
        }
    }

    // Check if the number is already present in the current 3x3 subgrid
    int startRow = row - row % 3;
    int startCol = col - col % 3;
    for (int i = 0; i < 3; ++i) {
        for (int j = 0; j < 3; ++j) {
            if (grid[i + startRow][j + startCol] == num) {
                return false;
            }
        }
    }

    return true;
}

bool solveSudoku(vector<vector<int>>& grid) {
    int row, col;
    bool isFilled = true;
    for (row = 0; row < 9; ++row) {
        for (col = 0; col < 9; ++col) {
            if (grid[row][col] == 0) {
                isFilled = false;
                break;
            }
        }
        if (!isFilled) {
            break;
        }
    }
    if (isFilled) {
        return true; // Grid is completely filled
    }

    for (int num = 1; num <= 9; ++num) {
        if (isSafe(grid, row, col, num)) {
            grid[row][col] = num;
            if (solveSudoku(grid)) {
                return true;
            }
            grid[row][col] = 0; // Backtrack
        }
    }
    return false; // No solution found
}

void printGrid(vector<vector<int>>& grid) {
    for (int i = 0; i < 9; ++i) {
        for (int j = 0; j < 9; ++j) {
            cout << grid[i][j] << " ";
        }
        cout << endl;
    }
}

int main() {
    vector<vector<int>> grid = {
        {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(grid)) {
        cout << "Solution:\n";
        printGrid(grid);
    } else {
        cout << "No solution exists.\n";
    }

    return 0;
}