题目：

Code:

#include <bits/stdc++.h>
//#ifndef ONLINE_JUDGE
//#pragma GCC optimize(2)
//#endif // ONLINE_JUDGE
using namespace std;

class Shudu
{
	bool nodes[10][10][10]; // Current block (i, j) can be filled by k
	bool row[10][10], col[10][10], area[10][10]; // Sum of numbers on a row/col/area
	int sum; // Sum of solved blocks
	public:
		int solved[10][10]; // Current status of table
		Shudu()
		{
			for (int i = 1; i <= 9; i++)
			{
				for (int j = 1; j <= 9; j++)
				{
					int x;
					cin >> x;
					for (int k = 1; k <= 9; k++) nodes[i][j][k] = !(bool)x;
					solved[i][j] = x;
					nodes[i][j][x] = (bool)x;
					row[i][x] = col[j][x] = (bool)x;
					sum += (bool)x;
				}
			}
			for (int i = 1; i <= 3; i++)
			{
				for (int j = 1; j <= 3; j++)
				{
					int x = 3 * i - 2;
					int y = 3 * j - 2;
					int p = 3 * i - 3 + j;
					for (int k = x; k <= x + 2; k++)
					{
						for (int l = y; l <= y + 2; l++)
						{
							area[p][solved[k][l]] = (bool)solved[k][l];
						}
					}
				}
			}
		}
		bool solve(int x, int y)
		{
			cerr << x << " " << y << endl;
			int cnt = 0; // Sum of solves
			int slv = 0; // One of solve
			for (int i = 1; i <= 9; i++)
			{
				int p = x / 3.1 + y / 3.1;
				nodes[x][y][i] = !(row[x][i] || col[y][i] || area[p][i]);
				cnt += nodes[x][y][i];
				if (nodes[x][y][i]) slv = i;
			}
			if (cnt) 
			{
				if (cnt == 1)
				{
					solved[x][y] = slv;
					sum++;
					return 0;
				}
			}
			else 
			{
				exit(1);
			}
			return 0;
		}
		bool judge()
		{
			return sum < 81;
		}
} shudu;

int main()
{
	while(shudu.judge())
	{
		for (int i = 1; i <= 9; i++)
		{
			for (int j = 1; j <= 9; j++)
			{
				if (!shudu.solved[i][j]) shudu.solve(i, j);
			}
		}
	}
	for (int i = 1; i <= 9; i++)
	{
		for (int j = 1; j <= 9; j++)
		{
			cout << shudu.solved[i][j] << " ";
		}
		cout << endl;
	}
	return 0;
}