This AMAZING Trick Can Solve Extreme Sudoku

[00:00:00]I will show you an amazing trick to solve this extreme Sudoku. And with that, it's solving time. You want to start by looking for digit restrictions from 1 to 9. You'll notice with the 1s, you're not going to be able to make any marks or solves right away.

[00:00:20]But with the 2s, you might notice here in block four, there's only two places for a two, so you can mark that with corner marking. And then, the same thing cuz of these 2s here in block eight.

[00:00:33]Greetings, friend. This Sudoku by Spef is perfect to show you an amazing Sudoku trick that works on some of the most extreme puzzles. I discovered this trick in 2022 and it changed everything for me.

[00:00:49]So, now you want to continue with the 3s.

[00:00:51]You'll notice with these two 3s, there's only two places for a three in block four. And then with these two 3s, only two places for a three in block eight.

[00:01:03]Nothing else you can do with the 3s. If you move on to the 4s, you might see with this four in the row and this four in the column, two places for a four in block two.

[00:01:15]And then with these two 4s, there's only two places for a four in block six, so you do want to mark that. No solves yet.

[00:01:22]You can tell this puzzle's pretty tough.

[00:01:25]All right, move on to the 5s.

[00:01:28]With these two 5s, only two places for a five here in block two. And then with these two 5s, only two places for a five in block six. And that's it for the 5s.

[00:01:42]Move on to the 6s.

[00:01:44]And you'll see with this six in the column and this six in the row, there's only two places for a six in block one.

[00:01:52]But since they're in the same row in this block, a six cannot be anywhere else in row three. This is called a pointing pair. So, sixes can't be here anymore. Because of this six in row one, you restrict the sixes to these three cells in block three. But, you don't want to mark that. You don't want to mark when there's two possibilities, cuz you're looking for that one step restriction. You solve one of these cells, you can solve the other right away for that marked cell. Okay.

[00:02:21]And then you can move on now to the sevens and notice similar situation with these two sevens. You have a pointing pair of sevens in block nine.

[00:02:32]Three spots here, so you don't want to mark that.

[00:02:35]Nothing else with the sevens. You move on to the eights. And you don't have any marked cells with the eights. You move on to the nines. And you might see with this nine and this nine, two places for a nine in block eight. And then in block nine with these two nines, two places for a nine right there. And that's it.

[00:02:58]There's no easy solves here. And now it's time to show you that amazing trick. But, first the question of the day. What did you do at this point in the puzzle? Did you find a way to solve the next cell? I'd love to hear what you tried. Please, please, please share in the comments and help me grow the internet's best Sudoku community. And so, it's time for that amazing Sudoku trick. And when you can't get anywhere with pairs and triples or single candidate strategies or bi-value cell strategies involving cells with just two possibilities, you want to look and think about setter's intent.

[00:03:38]What's the name of the puzzle? Lucid.

[00:03:41]Okay, that's something about light. And what patterns did Speth put in this starting grid?

[00:03:48]What might jump out to you is you have a one, two, and three here in block one.

[00:03:55]You also have a one, two, and three here in block nine.

[00:03:59]What does that do and how they interact?

[00:04:02]Well, you notice it puts a lot of pressure here in row one and column nine, right? Because one, two, and three can't be in these cells, they can only be in one of these four cells here in row one. But, a one, two, and three can't be in these cells either.

[00:04:19]They can only be in these four cells here in column nine.

[00:04:25]And so, that puts a lot of restriction.

[00:04:26]What you'll notice then is of the one, two, and three, only one of those digits, one, two, or three, can be outside of block three. Only one of them can be right here.

[00:04:37]So, that means two of the three digits would have to be in row one in block three.

[00:04:44]Same thing here. Only one of the digits, one, two, and three, could be in this cell because two would have to be right there.

[00:04:54]And if you put all three right here, well, you have a problem because then you only have one two places to put three digits. That's not going to work. So, you know that you have to have one of these digits outside block and you got to have at least two here and two here. The only way to satisfy that is that a one, two, or three has to be in this cell right here. It has to be at the intersection of the row and the column. I mean, you think about it. You put a one, two, three here, then one of those digits can be in this cell and then the other can be in this cell in the column. And then those other digits can be in outside the block in this row and in this column. This is called a Sudoku firework. It's an amazing strategy.

[00:05:43]Computer solvers don't notice it. They try to do a bunch of advanced strategies and make the puzzle seem extreme, but there's a couple of things you can do now with this firework. One, you know this has to be a one, two, or three in order to make all three digits fit in the row and in the column. Two, you also know these cells, and this is where most people get tripped up on the firework, these cells also have to contain digits one, two, or three. They have to be in these cells out here outside the block. Why?

[00:06:15]Because you can only have one of the one, two, or three right there.

[00:06:18]Cuz if you had two there, then you have not enough of those digits in the column.

[00:06:24]Same thing here. You can't put both the one, two, and three there. So, one of them has to be there, and then you know in this cell, one of these two cells has to be that third digit. One of these two cells has to be that third digit. So, really you can actually eliminate one, two, and three from these four cells as well.

[00:06:40]What we notice is that the four and five are marked right here, and the four and five are marked right there.

[00:06:46]Well, with the firework, just showed you, you cannot have any other digits other than one, two, or three in those three cells. So, what does that mean? It means you can displace those marks, and you can solve this cell now for four and solve this cell now for a five. You can displace those marks, and you can solve this cell for a five and solve this cell for a four. This is beautiful, beautiful logic. And now you have to be very careful on how you proceed and how you find the next solve.

[00:07:15]If you mess up one bit, you may have to start all over, and you don't want to do that.

[00:07:21]And so, now notice with these fours in these rows and these columns, there's only one place to put a four in block five.

[00:07:35]And then, you might see here with this six in this row, you have a pointing pair of sixes in block six. And so now with that pointing pair of sixes and these sixes, where can a six be here in block five? It can only be right there.

[00:07:52]So, you can actually solve that cell now for a six. And then notice with this seven in the column, you have a nice pointing pair of sevens. And if you're curious about how to learn more about pointing pairs and this marking, click on the pinned comment and get my free Sudoku solving guide. With this seven, pointing pair of sevens and this seven, only place for a seven in block five is right there. So, this next solve is very tricky to spot. You're actually going to find it here in block five.

[00:08:21]What you have to notice is that you have a three in this row, so a three can't be in that cell.

[00:08:27]You have a three in row nine, so a three can't be here and a three in row eight, so a three can't be there. So, where can a three be in this column?

[00:08:36]It's got to be right there. That's a hidden single three. It's the only possibility in column four, so you can make that solve.

[00:08:43]And now you can use this nine to notice that a nine's got to be in one of these two cells right here because of the nine already in the row.

[00:08:53]So, you have a pointing pair of nines, you can displace that nine and solve this cell now for a nine. And that is allows you to displace the nine in block nine and solve that cell now for a nine.

[00:09:05]And then follow these nines and this nine, only place for a nine in block three is right there. And then with these nines and this nine, you can solve this cell for a nine displacing that six.

[00:09:19]Okay. And after doing that, now notice where can an eight go in block one?

[00:09:23]Well, with this eight in the row, an eight has to go right there. And then with these two eights and this eight, you can solve for an eight in block three. But hey, go back to the scene of the crime. You only have three digits remaining here in block one.

[00:09:38]Four, five, and seven. They're in the row and in the block. This is called a locked triple and it's going to allow you to remove a four, five, and seven from every other cell in this row. And so, what that means is these cells right here, they got to be a one, two, and three. You already marked those two. The two and three's right there. This is a naked single one. So, you can solve that first one and it leaves you with a two, three naked pair.

[00:10:05]And then look here in block six. Now that you've made some of these marks, you might notice with these two ones, you can solve this cell now for a one.

[00:10:14]Leaves you with a two, three, and a six with this three in the row.

[00:10:17]That's got to be your three with this two in the column. That's got to be your two displacing that six. And now you solved block six. Where can you go from here?

[00:10:28]Try to solve block three now. Okay, you got a one, two, three, four, six, eight, nine in this column. You need a five and a seven. With this five in the row, that's got to be your five. That's got to be your seven. And it leaves you with just a two, a three, and a six. With the two and the three in this column, that's got to be your six. This two in the row allowed you to solve this for the two and that's going to be your three.

[00:10:56]And now with this two, you can solve this for a three. With this seven, you can displace that seven. Solve this cell for a seven now. And you might think you're stuck here with the one and the two, but you can actually do a little bit better than that.

[00:11:10]Because you might see with this two in row five, you have a pointing pair of twos in block five. A lot of pointing pairs.

[00:11:19]Since the two's got to be one of these two cells, you can remove the two from this cell.

[00:11:23]Solve that for a one. Solve this cell now for a two.

[00:11:28]Displace this two. Solve this cell for a two.

[00:11:31]Don't see a one in column four, so you know you can solve that cell for a one right away.

[00:11:38]And now follow this one here, and you can solve for one in block five. Follow these ones and this one, solve for one in block four, displacing that three, so you can solve that three right away.

[00:11:52]And then you can follow these ones down with this one, solve for one in block seven.

[00:11:59]Okay, you want to look at the places where you have most of the digits filled out. So, in row five, you have a one, two, three, four, five, six, seven, you need eight and a nine.

[00:12:09]Well, the eight can't be here, so this has to be your eight, and that's going to be your nine. And since you displace the nine, you know you can solve that for nine, and with your marking, you know that's a two right away, allowing it to displace this two and solve this cell for two now.

[00:12:24]You have two digits remaining in block four.

[00:12:27]One, two, three, four, five, six, you need a seven and an eight. Well, this eight tells you the eight goes right there, and the seven goes right there.

[00:12:37]And now you can remove the seven from this cell.

[00:12:39]Need a four and a five to finish column three. Well, with this four, you know that's the five.

[00:12:45]That's going to be the four, that's going to be the seven, that's going to be the five to finish block one. So, you just want to tackle these blocks one at a time, look where you have the greatest restriction. Right here, you just have two cells remaining in column two. So, you have a one, two, three.

[00:13:00]You're missing a four, and you're missing an eight.

[00:13:03]Don't see a way to solve both of those just yet. Over here, it looks like you need a seven and a six. With this seven, there's your seven, and there is your six. This seven allows you to displace that seven, solve this cell for seven now.

[00:13:18]Six and an eight right here. You know, with this six, that's got to be the eight. That's got to be the six. With this three, you can displace three, solve this cell for a three now.

[00:13:30]Okay.

[00:13:31]Move on here in column nine. One, two, three.

[00:13:35]Need a four and a five. With this five, there's your five, there's your four.

[00:13:39]Now, you can disambiguate the four and the eight right there. Beautiful. Don't see an eight in block eight. So, that's got to be your eight, and your last cell is a six.

[00:13:48]Now, see how many extreme Sudoku tricks you can learn in this playlist. Thank you so much for watching.