Sudoku Strategy and Tips

If you have been looking for a simple Sudoku strategy and tips to help you solve these puzzles, this article will give you a basic guidebook approach in an illustrated manner. There are three basic Sudoku strategies to follow. A tip here is following each in succession to eliminate number choices using logic.

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The One and Only Choice Strategy :
When you first look at a Sudoku puzzle you may wonder If there are enough given numbers to solve the puzzle. You will notice that there are many regions, or columns, or rows without any numbers filled in. These will fill themselves in by using the process of elimination.

In the example below a useful tip for Sudoku strategy is to quickly look for the missing number within a given column, or row, or region. When you look through the area of choice, count from 1 to 9, looking for the missing numbers.

Fig 4

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7
6	7		2	6		1			8
7	2
8	5				3	2		9	4
9		8	7		1	6	3	5

Fig 5

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7
6	7		2	6		1			8
7	2
8	5				3	2		9	4
9		8	7		1	6	3	5	2

Fig 6

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7
6	7		2	6		1			8
7	2
8	5				3	2		9	4
9		8	7		1	6	3	5	2

Look at the bottom row and the farthest right column. Make note of which numbers are missing in each. You'll notice that the row is missing 9,4,2 while the column is missing 7,5,2. Notice that the 2 is the common number. The first tip in using this Sudoku strategy is to find where the 2 goes.

Start where the column and row intersect in the corner, taking each number and eliminating the number if it is duplicated elsewhere in either the column or the row. The 2 is the only number not duplicated in either the row or column. This makes 2 the only choice for that corner. Now take each remaining number and repeat the process for the column and again for the row. Using this Sudoku strategy as a tip to the remaining puzzle will help lay out the rest of the grid.

Scanning :
The next tip is a Sudoku strategy called Scanning. This strategy will help solve the most basic or the most complicated puzzle. In the example below, we take the number 2 again. This time we look for every occurrence of that number. Remembering the rules of Sudoku, you find that any row, column, or range that has a 2 in it becomes ineligible to place that number. The red lines show all the ineligible slots.

After you locate all locations of a number, locate a row where the number doesn't appear. In the example below we use the number 2 again. The red marks all the slots where 2 can't go because there is another 2 in play. The one slot shaded green is the only available spot; again using scanning and elimination to find the correct place.

Fig 7

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7			2
6	7		2	6		1			8
7	2
8	5				3	2		9	4
9		8	7		1	6	3	5	2

Fig 8

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7				5
6	7		2	6		1			8
7	2								7
8	5				3	2		9	4
9		8	7		1	6	3	5	2

Fig 9

	A	B	C	D	E	F	G	H	I
1	9				6				3
2	1		5		9	3	2		6
3		4			5				9
4	8						4	7	1
5			4	8	7			2	5
6	7		2	6		1			8
7	2								7
8	5				3	2		9	4
9	4	8	7	9	1	6	3	5	2

Another use of Sudoku strategy is the tip of scanning for obvious numbers in rows, columns, or ranges. In the next example, the shaded row is missing the 2,5, and 7. We already have the two from the strategy used above. Using scanning, you can locate the one spot where 7 can't go, so then using elimination it becomes clear where the 5 and 7 are in the row order.

Now let's look at the row across the bottom. You already have the 2 in place. The remaining missing numbers are 9 and 4. Following the rules of Sudoku you note that the 9 up in R1C1 eliminates the cell at R1C9 for that number. This only leaves the number 4 for that slot. The only slot left in this row is filled by the 9.

When you use the scanning Sudoku strategy, a helpful tip is to be systematic with the puzzle solving. Scan for the numbers in sequence from 1 to 9, and eliminate each number from all grids before moving on to the next.

Now you have two Sudoku strategies for solving. Another tip, not every puzzle can be solved using these strategies. Some puzzle solutions will halt when you cannot solve any further because more than one number can fit in a slot. This brings a third strategy into play.

Eliminating Candidates :
As a tip, the Sudoku strategy of eliminating candidates is one of the basic components to solving these puzzles. To make this strategy effective, you will need to find all of the possibilities for missing numbers in each slot.

The process of elimination involves finding what are known as naked and hidden number combinations. These are often referred to as 'naked and hidden singles', 'naked and hidden doubles', 'naked and hidden triples' and 'naked and hidden quads'. Simply stated, this means that a number, or group of numbers can fit into more than one slot in the grid. Using the process of elimination you can logically cross off each of these numbers to find the right solution.

Locked Candidates :
There are times when a candidate within a 3x3 area is restricted to only one row or column. When this happens you can remove the number from the remaining cells in that row or column which is outside of the 3x3 area.

Another type of locked candidate can be found within a 3x3 square when the number is restricted to one row or column. When this happens, you can remove that number from the remaining cells that are inside the square.

These are the simple Sudoku strategies. The tips in this article can help you on the way to solving any level of Sudoku puzzle.