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

Difficulty: Very easy (0)

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

Difficulty: Easy (0)

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

Difficulty: Hard (0)

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

Difficulty: Very easy (0)