Pattern: L Pattern

This pattern has the potential to find lots of numbers

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When you see an L pattern you will often be able to find twins and/or triplets using it. You will also find where other numbers go even if you can't solve the twins and triplets you find. Just knowing about them can help you.


The L pattern exists when there is a wall that has one populated cell adjacent to it. The wall and the adjacent cell must be in the same box. There are two L patterns, one in box 1 and one in box 3, in the figure below.

Sudoku grid partially filled, with an L pattern in boxes 1 and 3
Figure 1

NOTE: the puzzle in the figure above is not valid - it is only used to illustrate the L pattern

Let's see how much information we can get from this example. Look at figure 1. The 1524 in box 1 is an L pattern. The 1347 in box 3 is also an L pattern -- the 3 can be in any cell in box 3 column 8.

Let's look at box 1 first. Notice that there is a 6 and a 7 in box 7 that can only go in column 2 in box 1. The L pattern helped identify those 67 twins in box 1. The twins can't be solved yet. But that also helps us find triplets in box 1 column 3. The triplets in column 3 are 3, 8 and 9. Although we can't solve them, because of the L pattern we were able to identify in which column every number goes in box 1.

Now look at boxes 4 and 7. The twins and triplets in box 1 will help us find numbers in these boxes too.

Sudoku grid like the one in the previous figure with more numbers filled in, in red

Figure 2

NOTE: the puzzle in the figure above is not valid - it is only used to illustrate the L pattern

Figure 2 shows all of the numbers found because there is an L pattern in box 1 (red numbers). Make sure you understand how each of these numbers were solved.

Extra Credit!

It was mentioned above that box 3 also has an L pattern. As an exercise see how many numbers you can find by looking at the L pattern in that box.

Video about the L pattern

Watch this video for more info and examples of the L pattern

See more videos illustrating the L pattern in the video index -- videos 58, 75 and 81.

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