Congrats to Will Norris ’19 for completing Boss Level 2! If you have any questions feel free to email him at email@example.com
As for Level 3, I must regrettably inform you that I’m pulling a Harry Potter Deathly Hallows on you. Yes, I am breaking it into two parts… I realized I had a lot to cover. I’m also writing this in the Info Commons the day before publishing because my computer at home is broken…
Without further ado!
This lesson should really be with 2.2. I forgot. I’m such a slacker :(
Anyways, 2.2 was the Naked Pair, 3.1 is the Hidden Pair
The name of the tip, Hidden Pair, is kinda self-explanatory. Take a look at the third row – maybe you can get it without explanation.
Notice how the 6th and 9th columns are the only boxes in row 3 that have both a 1 and a 3.
Since this is basically the same as 2.2 I’m not going to spend much time explaining this:
- If column 6 is a 1, column 9 must be a 3, and vice versa.
- The only 1s and 3s in row 3 are in columns 6 and 9.
- So you can eliminate all other candidates from those two boxes.
Now it’s time to level up. I don’t use this next strategy too often when I do the puzzles on the Dallas Morning News or this app, but this really helps with understanding tougher strategies. It’s called the X-Wing.
For this guy, we are gonna be focusing on the 7s. Especially the ones in rows 2 and 6.
Notice how there are only two possible places for 7 to be in each of these rows.
Conveniently, these possibilities line up with each other!
It’s super important that these are the only 7s in the row. If there are more 7 candidates in the row, trying to do the X-Wing will mess you up.
Since there are only two though, we are left with two possibilities for each row. Either the 7 is in column 4 or it’s in column 8.
Let’s run through these possibilities just like we did in 2.2.
Now that we have our two cases, we can eliminate some candidates. Remember that what is crossed out in both cases must be true no matter what.
The red Xs mark the candidates that can’t be true because we placed the 7 in row 6 column 4.
We eliminated one of the two 7 candidates in row 2. So row 2 column 8 must be a 7 (written in green).
The blue Xs denote eliminated candidates due to the green 7.
Below I did the same thing for the second possibility.
As you can see a lot of the Xs are shared, which means they are true no matter what:
A solid 8 candidates obliterated!
How awesome is that!
Summary of 3.2
- There must be exactly two candidates of a number in a row
- There must be exactly two candidates of the same number in a different row
- The candidates from these two rows must line up.
- You can eliminate all candidates from these two columns except from the two original rows
The same is true if you switch rows and columns
It’s hard to be concise without getting technical. So I wrote a lot for the lesson in hopefully-simple words and wrapped it up in a complicated list. But it should make sense if you’ve been following me so far.
I haven’t gotten any emails about it being hard to understand. But I don’t think many people have been reading the past lessons because they were so simple to begin with… Now’s the time to start reading the lessons because more difficult tricks are way too hard to understand if you don’t already know this.
So we’re looking at 7s again.
Rows 3 and 7.
Unfortunately, there is no X-Wing because row 7 has four 7 candidates.
But let’s pretend it’s an X-wing, a fake-X-Wing, more commonly known as a finned X-Wing.
Here’s our first case. Let’s just pretend columns 7 and 8 don’t exist for a second (if this still feels unnatural and wrong to you, you’ll have to get used to hypothetical cases. They aren’t going away…)
Since those columns are gone, we have an X-Wing between the 7 candidates in rows 3 and 7 (circled in blue).
If you don’t know where those red Xs are coming from, please read 3.2 first.
But these red Xs aren’t necessarily true. We made an assumption, but we haven’t covered all the cases…
So either the X-Wing is true… Or there is a 7 in row 7 column 7 or 8.
So now we’ve covered all the cases. What do they have in common?
Yep… We just did all that work, only to get rid of a single candidate… Sorry if that was a little anti-climactic for you.
This is actually great though because X-Wings are so much more versatile.
Boss Level 3
Sorry for cutting this week’s level a little short. I tried to do it justice. Hopefully, you don’t think it was as useless and irrelevant as Deathly Hallows Part 1…
I promise next time will be good!
Have fun solving this one my growing grasshoppers!
Again, the first person to email me (firstname.lastname@example.org) a correct solution will be featured in next week’s episode.
If you can solve this and Boss Level 2 without any help, I am fairly confident you can solve all of the 5 star Sudokus on the Dallas Morning News. There is only one level left (5 outlined stars)! Nice job :)
Happy Sudoku-ing, and see you next week on The Roundup!