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

Difficulty: Very easy (0)

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

Difficulty: Very easy (0)

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

Difficulty: Very hard (0)

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

Difficulty: Very easy (0)