9	8		5	7
2			6	4		9
			4			1		2
		2	9				7	8
	6	5				8	9
3	7				9	2
8		4			3
		3		2	1			4
				1	4		2	9

Difficulty: Very easy (0)

			2	7		9		5
2			4		5		7
	1	8		3			5
					9	4	6
			7		8
	5	3	1
	8			9		6	4
	4		9		1			6
8		1		6	2

Difficulty: Medium (0)

6					1		2
5	8	9	1		3	2
	2		5				6	1
2	3	7						5
			7	3	4
9						8	1	4
7	1				9		3
		1	3		5	4	7	2
	4		8					7

Difficulty: Very easy (0)

		5	6		9	2	8
	6		8				4
2		6				1
4			1	3		6
6	4	1				9	2	8
		7		2	5			9
		2				5		6
	9				6		3
	2	3	9		7	8

Difficulty: Very hard (0)