关于数独游戏的C++解法

#include <iostream>
using namespace std;

void readAPuzzle(int grid[][9]);
bool search(int grid[][9]);
int getFreeCellList(const int grid[][9], int freeCellList[][2]);
void printGrid(const int grid[][9]);
bool isValid(int i, int j, const int grid[][9]);
bool isValid(const int grid[][9]);

int main()
{
  // Read a Sudoku puzzle
  int grid[9][9];
  readAPuzzle(grid);

  if (!isValid(grid))
    cout << "Invalid input" << endl;
  else if (search(grid))
  {
    cout << "The solution is found:" << endl;
    printGrid(grid);
  }
  else
    cout << "No solution" << endl;

  return 0;
}

/** Read a Sudoku puzzle from the keyboard */

void readAPuzzle(int grid[][9])
{
  // Create a Scanner
  cout << "Enter a Sudoku puzzle:" << endl;
  for (int i = 0; i < 9; i++)
    for (int j = 0; j < 9; j++)
      cin >> grid[i][j];
}

/** Obtain a list of free cells from the puzzle */
int getFreeCellList(const int grid[][9], int freeCellList[][2])
{
  // 81 is the maximum number of free cells
  int numberOfFreeCells = 0;

  for (int i = 0; i < 9; i++)
    for (int j = 0; j < 9; j++)
      if (grid[i][j] == 0)
      {
        freeCellList[numberOfFreeCells][0] = i;
        freeCellList[numberOfFreeCells][1] = j;
        numberOfFreeCells++;
      }

  return numberOfFreeCells;
}

/** Display the values in the grid */
void printGrid(const int grid[][9])
{