Locked Candidates

Locked Candidates is the next technique to use after Naked/Hidden Pairs and Triples.

They can sometimes be easy to spot, but you will normally have to deliberately look for them.

Let's look at the 6 candidates in this column. There are only 2 cells we can insert the 6 for this column.

Further, they are both in the same region.

From looking at the row, we know that one of the two highlighted green 6 values must be the location of the 6.

We don't know exactly which one at the moment, but we know it will be in one of those two cells.

This means we can remove all other 6 candidates in this region.

This type of Locked Candidates is called 'Claiming'.

This is another example of a Claiming Locked Candidate.

In the 8th column, all the possible locations for the 8 are in the top-right region, i.e. one of the two green highlighted 8 candidates has to be the location of the 8 in this column and region

This means we can remove all other 8 values from this region.

This example of Locked Candidates is slightly different, but the principle is exactly the same.

If we look at the region first in this example, we know the top-left region must contain a 3.

In this example, all the 3 candidates for this region appear in the second row.

This means we can remove all other 3 candidates from this row.

This type of Locked Candidates is called 'Pointing'.

Can you spot the Locked Candidate in this puzzle?

Did you spot it?

Can you spot the Locked Candidate in this puzzle?

Did you spot it?

Can you spot the Locked Candidate in this puzzle?

Did you spot it?

That's everything you need to know for Locked Candidates!

Practice puzzles

Here are 10 Sudoku puzzles where you will need to apply the Locked Candidates technique to solve (in roughly increasing difficulty),

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