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

bool isValid(const int grid[][9]);
bool isValid(int i, int j, const int grid[][9]);

int main()
{
int grid[9][9];

cout << (isValid(grid) ? "Valid solution" : "Invalid solution");

return 0;
}

/** Read a Sudoku puzzle from the keyboard */
{
cout << "Enter a Sudoku puzzle solution:" << endl;
for (int i = 0; i < 9; i++)
for (int j = 0; j < 9; j++)
cin >> grid[i][j];
}

// Check whether the fixed cells are valid in the grid
bool isValid(const int grid[][9])
{
for (int i = 0; i < 9; i++)
for (int j = 0; j < 9; j++)
if (grid[i][j] < 1 || grid[i][j] > 9 ||
!isValid(i, j, grid))
return false;

return true; // The fixed cells are valid
}

// Check whether grid[i][j] is valid in the grid
bool isValid(int i, int j, const int grid[][9])
{
// Check whether grid[i][j] is valid at the i's row
for (int column = 0; column < 9; column++)
if (column != j && grid[i][column] == grid[i][j])
return false;

// Check whether grid[i][j] is valid at the j's column
for (int row = 0; row < 9; row++)
if (row != i && grid[row][j] == grid[i][j])
return false;

// Check whether grid[i][j] is valid in the 3-by-3 box
for (int row = (i / 3) * 3; row < (i / 3) * 3 + 3; row++)
for (int col = (j / 3) * 3; col < (j / 3) * 3 + 3; col++)
if (row != i && col != j && grid[row][col] == grid[i][j])
return false;

return true; // The current value at grid[i][j] is valid
}
```