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Sudoku Hidden Patterns

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Introduction

Sudoku hidden patterns can be quite useful. They can help find numbers in subtle ways. This page explains hidden patterns and gives examples.

Below the detailed example, there are more hidden pattern example images which should give you enough information to find hidden patterns yourself.

Detailed Example

The "Hidden" pattern isn't an actual pattern, but a combination of a pattern (that you may already be aware of), and a set of numbers that happen to strategically occupy two cells in the same box. The result changes the pattern to a different pattern.

At this point, you may be asking yourself - what??? An illustration may be very helpful. Consider the following puzzle.

Figure 1

In Figure 1 there is a 3 and a 6 in box 7. These two numbers form a diagonal pattern. We also have 27s in column 3 and in row 7. The 27s in these two places give us 27 twins in box 7. Figure 2 below shows where the 27 twins are.

Note that we can't solve the 27s in box 7. There isn't enough information to tell us where the 2 and 7 go, but we know that they must go in cells r8c2 and r9c1.

Figure 2

This gives us an interesting situation. The diagonal pattern in box 7 can now be viewed as a Corner pattern instead of a diagonal pattern. This is what is called a hidden pattern.

Because of the hidden corner pattern, you should be able to see that the 9 in box 4 goes in r6c1. We know this because the 9 cannot go in r9c1 because that is a 2 or a 7.
Watch video showing this puzzle getting solved

Other Sudoku Hidden Patterns

Here are a few examples of other hidden patterns.

Figure 3

This example shows a hidden corner pattern in box 3. The green circles indicate where 34 twins are. The 34 twins can't be solved, but they complete the corner pattern in box 3.
Watch This video to see this puzzle get solved.

Figure 4

Look at figure 4. There are 47s in both row 5 and column 5, so the green circles are 47 twins. This changes the opposite pattern to a hidden plus pattern in box 5. The 59s in column 5 are now 59 twins in box 5, and a 9 can be placed in r6c3 in box 4.
Watch Video 166 which shows how this puzzle is solved.

Figure 5

This last example is trickier, but shows you how powerful hidden patterns can be.

We start with 23 twins in column 1 (the twins are in cells r2c1 and r7c1, marked with red circles). After the 23 twins are found, there are three numbers left in column 1 (6, 7 and 8). The cells marked with green circles can have all three candidates - 6, 7 and 8. A 2 cannot go in either of those two cells, so the only place a 2 can go is in row 7, column 1 or 3. This makes box 7 a T pattern, as far as the 2 is concerned.

Because the 2 is constrained to row 7 in box 7, we can find a 9 in box 9. Note that there is only one empty cell in box 9 row 7. That cell can only be a 2 or a 9. Because the 2 is constrained to box 7, we know that the 9 goes in row 7 box 9.
See video 283 to watch this puzzle get solved.

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