Frank Puzzles About Checking High and Low | Easy Variant Sudoku

Ajouté : 2026-05-05

[00:00:02]Hello everyone. I'm Frank and welcome to Frank Puzzles and this is today's easy level puzzle and take that easiness with a grain of salt because it's considered easy by the people on the Logic Masters Germany Forum and there's a lot of really smart people there.

[00:00:18]Today's puzzle is called checking high and low and it's by Snepix.

[00:00:23]And here are the rules.

[00:00:26]We have normal Sudoku rules apply which means in every cell in the grid place a single digit such that every row, column, and designated nine-cell region contains the digits one through nine exactly once each.

[00:00:43]We have thermometers where digits along a thermometer increase from the bulb to the tip.

[00:00:51]So for example, you could have something like say three, four, seven, nine here. And that would be valid because it's continuously increasing from the bulb to the tip.

[00:01:02]What we could not have is something like say three, four, seven, six because from the seven to the six you are decreasing and you can never decrease along a thermometer.

[00:01:14]So that's an example of how thermometers work and we also have German Whisper Lines um or as I like to call them Whisper Five Lines which a setter came up with and I thought it made a lot of sense because it's very easily extensible.

[00:01:30]Anyways, um on these German Whisper {slash} Whisper Five Lines you'll notice it says adjacent digits along a green line must have a difference of at least five. So say as an example we had a three here, then this digit would have to be eight or nine because the only digits which are five or more away from three are eight and nine.

[00:01:53]And that's an example of how Whisper Five Lines work and I will be calling them Whisper Five Lines because as I said I thought the naming that the setter came up with was very easily extensible.

[00:02:06]And those are all the rules. If you'd like to play along, there's going to be a link in the description and now I'm going to get started.

[00:02:16]Let's go.

[00:02:20]Okay, the one thing that I see almost immediately is row three.

[00:02:27]Um In row three first of all six of the digits are on a Whisper Five Line.

[00:02:43]Five can never be on a Whisper Five Line because if you subtract five or more from five you get zero or less. If you add five or more to five you get 10 or more and none of which are normal Sudoku digits. So five has to be one of these three digits. Well five cannot be here because it that would force this to be six, seven, eight, nine, 10 and 10 can't be a digit.

[00:03:09]And five can't be here because that would force this to be four, three, two, one, zero and zero is not a normal Sudoku digit. So where is five? It has to be here. Since that's five, that forces this to be four, three, two, and one.

[00:03:25]That means one can't be anywhere here.

[00:03:31]Well there's six as a digit can only be next to one on a Whisper Five Line.

[00:03:40]So if any of these were six, you would guarantee one has to be next to it on a Whisper Five Line and we can't have one in this row. So these cannot be one here.

[00:03:52]Where Sorry, these can't be Well, they can't be one which means they can't be six here. Where is the six in the row?

[00:03:58]It must be here.

[00:04:02]So these combination of digits are two, three, four and seven, eight, nine.

[00:04:12]Four on in row three has to be next to a nine.

[00:04:17]So four can only be here and here Oops.

[00:04:21]Four can only be here or here or here or here because four can only be next to one unique digit on a Whisper Five Line.

[00:04:30]And so the nine would have to be one of these two digits.

[00:04:35]Well that means the other high digits on in row three have to be seven and eight.

[00:04:43]Um they cannot obviously be next to the nine. So what do they have to be next to? They have to be next to a unique digit of a two here.

[00:04:53]So this is three, four, seven, and eight. This is three, four, seven, and eight.

[00:05:00]Um If this is nine this cannot be low as two, three, four so it would have to be one that it's next to.

[00:05:12]Um and this is because on a Whisper Five Line you'll always alternate between low digits and high digits on a Whisper Five Line.

[00:05:21]Um hm Um and uh you'll look I've said this many times before particularly in the Learn How to Sudoku series. So if you are curious about why that is, um just check out one of my Learn How to Sudoku series with German with Whisper Five Lines in them.

[00:05:49]Two cannot be next to seven or eight because they would have to be with it in the same row. So therefore this would be nine as a possibility. So this is one or nine.

[00:06:02]So I think we're guaranteed a nine has to be one one of these two digits, right? If this is two, this is seven and eight. This can't be six next to the two, it would have to be nine.

[00:06:13]So nine has to be one of these two digits and nine has to be one of these two digits here.

[00:06:18]Um What about this Whisper Five Line? We don't have one and two available. So if this is low, it would have to be three next to eight or nine here.

[00:06:30]If it's not three in the middle, it has to be three and four on the outside which forces a nine to be in the middle.

[00:06:38]So therefore we are guaranteed a three here or a nine and a nine here. So this can't be three or nine here. If it's low, it's four.

[00:06:52]If it's high, it could be six, seven, or eight.

[00:06:56]So four would have to be next to nine.

[00:06:58]Six, seven, or eight would be next to one, two, or three. But this can't be three because of three in the column.

[00:07:06]So if this is four, nine, this would be one, two, or three. If this is six, seven, or eight, this would have to be next to one, two, or three.

[00:07:17]Um but it could be six through nine here. So that's pretty wide open.

[00:07:22]Um This is a thermometer but this is eight as the largest digit. So if this is eight at most, this is seven at most, six at most, five at most, four at most, three at most.

[00:07:37]Which means this is one, two, three, two, three, four, three, four, five, four, five, six, five, six, seven, or six, seven, eight there.

[00:07:46]>> [snorts] >> This cannot Okay, we have seven, eight, nine remaining in box one. This can't be nine because of nine in the column.

[00:08:01]Remaining digits of row two are five, six, seven, eight.

[00:08:06]Okay.

[00:08:10]Um Um what about this thermometer?

[00:08:25]This can't be nine so we have eight at most, seven at most, six at most, five.

[00:08:30]So this is one through five, two through six, three through seven, and four through eight here.

[00:08:39]Remaining digits of row one are one through six.

[00:08:51]Um hm Neither of these can be nine.

[00:08:58]So therefore four can never be here.

[00:09:05]Um these are opposite sets.

[00:09:09]These are the same set.

[00:09:12]So this can't be nine. So we have one, two, three, six, seven, eight potentially there.

[00:09:24]Um remaining digits of column one no one, two, three or nine so it's four, five, six, seven, eight.

[00:09:34]We know five has to be one of these two digits because it can't be on the Whisper Five Line and we already know where five is in box one.

[00:09:44]So five has to be one of these three digits there.

[00:09:52]Hm >> This cannot be four here, so this must be what? 1 2 3 6 3 9.

[00:10:07]It's still pretty broad.

[00:10:12]Um Oh.

[00:10:30]Um Hm.

[00:10:51]Let's just mark this as one color.

[00:10:58]So, we'll make this yellow, and these have to be opposite sets.

[00:11:06]Therefore, this is the other one, and this is the yellow set.

[00:11:13]Does that help us any? Not particularly.

[00:11:16]Hm.

[00:11:23]>> [snorts] >> Hm.

[00:11:34]Hm.

[00:11:45]Well, we know this is low, we know this is high.

[00:11:50]That doesn't really help us much, though.

[00:12:00]Uh well, one thing is this cannot be three and this can't be four here. If this is four, that forces this to be three, which makes that two and one here, but that would four eliminate one and two here. So, this would guarantee that's nine.

[00:12:15]So, this can't be four, but that doesn't tell us too much, right?

[00:12:24]Hm.

[00:12:26]Hm.

[00:12:39]Hm.

[00:12:40]Hm.

[00:12:45]This is also low.

[00:12:48]Hm.

[00:12:58]This can't be two for the same reasoning, because if this is two, that's one, that would force both of these to be nine. So, this can't be two, that can't be three, no four, no five, no six there.

[00:13:10]Okay.

[00:13:24]Six and seven are high. Aha.

[00:13:28]We are guaranteed two highs here and one high here, and this cannot be nine.

[00:13:34]So, that means this is 6 7 or six can't be next to two unique digits on a whisper five line. And these would both be next to two unique digits on a whisper five line.

[00:13:44]Therefore, we are guaranteed this must be seven or eight here, this must be seven or eight here. So, this cannot be seven or eight here because of seven or eight pair in the column. So, that's six, that makes this five, four, and three, which means this cannot be three here.

[00:14:04]Six eliminates six in the rest of the column, five eliminates five in the rest of the column.

[00:14:11]Um remaining digits of column eight are 1 through 5, and this can't be five because of five in the box.

[00:14:21]Um Hm. Three eliminates three here.

[00:14:29]So, this is one or two, this is one or two, that eliminates one and two in the rest of the box or rest of the column.

[00:14:36]So, this can't be one, two, or three.

[00:14:38]Remaining digits in column five are four through eight.

[00:14:43]This can't be four because of four in the box, this 4 5 6 eliminates 4 5 6 in the rest of the column. Sorry, rest of the row. Where is five now? We have Well, we have a 7 8 7 8 pair in column one, which eliminates 7 8 in the rest of the column.

[00:15:01]So, this can't be seven or eight. Where is the five? It can only be here. That means this cannot be eight here, so this must be three and four surrounding the nine here.

[00:15:13]Because there's no other high digits possible to be next to the three.

[00:15:17]So, this is nine.

[00:15:20]This is 3 4 as a pair, which eliminates 3 4 in the rest of the column. This can't be four, it's six.

[00:15:27]That's only next to one on a whisper five line, this can't be one then, so it's two. That leaves this as 7 8 or 9.

[00:15:37]Okay. Nine eliminates nine from being here.

[00:15:43]Um hm.

[00:15:47]Five eliminates five from being there.

[00:15:52]This is low, this is high. Hm.

[00:15:59]Where is three in box four? Cannot be here because of three in the row, can't be here because of three in the column.

[00:16:05]This is a high digit, so this must be three there.

[00:16:09]That means this can't be three there.

[00:16:11]>> [clears throat] >> Where is four in box four? Can't be here because of four in the row, can't be here because of four in the column. So, it has to be here.

[00:16:21]Remaining digits in box four are 2 7 8 9.

[00:16:29]Um Four eliminates four here. This is 1 2 as a pair or as a possibility, one of these has to be one or two. This is one or two, that eliminates one and two in the rest of the column. So, this can't be one, two, this can't be one, two, these can't be one, two, we are guaranteed this low has to be a three.

[00:16:49]Three can only be next to eight on a whisper five line out of seven or eight, so this is 3 8 as a pair. That eliminates 3 8 in the rest of the box and column.

[00:17:02]Um This can't be if this is three, it can only be next to eight and nine on the whisper five line. So, cannot be next to these two digits, so this is one or two, which means it must be next to eight here, which makes that next to a three here, which makes that next to a nine there.

[00:17:27]That means it can't be eight, it's seven, no seven here.

[00:17:35]Three eliminates three here, so that's four, which makes this three.

[00:17:40]That eliminates three in the rest of the row.

[00:17:45]So, three in row eight has to be one of these two digits because it can't be here.

[00:17:51]Can't be here because of three in the box, can't be here because of three in the box.

[00:17:58]Okay.

[00:18:06]Remaining digits of column two, we have 2 5 7 8 9, but no nine available.

[00:18:15]This can't be eight because of eight in the row.

[00:18:18]Remaining digits of column three are 1 2 6 7 8 9, and this digit cannot be one or two because it must be greater than that digit, which is two at minimum.

[00:18:34]Um this can't be eight. None of these could be nine because of nine in the box, this digit must be smaller than that one, cannot be eight.

[00:18:43]So, this is 6 7 or 8 there.

[00:18:47]And this can't be eight because of eight in the row.

[00:18:54]Four eliminates four from being here, this can't be four, so if this is low here, that must be three here, which makes that four there.

[00:19:06]Um hm.

[00:19:09]Remaining digits of row six, we have 1 7 8 9 here, and it can't be seven because we have a guaranteed seven here because seven's eliminated from that possibility in box four from being here.

[00:19:25]So, it's 1 8 and 9.

[00:19:31]Um Hm.

[00:19:38]Remaining digits of row five, we have 3 4 5 8 9.

[00:19:51]Well, this can't be three or four because of three or four in the box. We have 5 8 9 as a triplet, which eliminates 5 8 9 in the rest of the row. So, this is three or four. This is three or four.

[00:20:04]These are all lows.

[00:20:11]We have five guaranteed to be one of these two.

[00:20:15]One's guaranteed to be one of those two.

[00:20:20]Um 6 7, these are all highs. I'm not sure if coloring them is very useful right now.

[00:20:30]This is guaranteed to be high.

[00:20:38]Huh.

[00:20:39]Okay.

[00:20:45]Remaining digits of row four are 1 2 6 7 8 9.

[00:20:55]No seven here.

[00:20:57]No nine here because of nine in the column and seven in the box because of the seven.

[00:21:07]This is high.

[00:21:10]Is that helpful? Not particularly.

[00:21:14]6 7 8 is high.

[00:21:17]Hm.

[00:21:31]>> [snorts] >> Um hm.

[00:21:40]Where Well, four cannot be here or here.

[00:21:45]So, four is one of these four.

[00:21:48]But, that doesn't really restrict very much.

[00:21:53]Uh where is nine in box eight?

[00:21:58]Can't be here because of nines in the row. Can't be here because of the thermometer. Can't be here because we guaranteed a nine here, so nine has to be here.

[00:22:07]Which eliminates nine in the rest of the column.

[00:22:16]Interesting.

[00:22:18]Hm.

[00:22:20]This Well, well, could be seven.

[00:22:30]Hm.

[00:22:36]Uh Um hm.

[00:22:44]No, two is one of these two.

[00:23:15]Hm.

[00:23:19]Remaining digits of column or box nine have to be 1 2 4 5 6 7.

[00:23:29]No five here because of five in the column.

[00:23:35]That's pretty much all we have.

[00:23:37]No four here because of four in the row.

[00:23:43]Hm.

[00:23:49]Oh, two's here.

[00:23:51]Which eliminates two here, so that's nine. That makes this one. Okay.

[00:23:56]So, the yellows are all highs.

[00:23:59]And the pinks are all lows.

[00:24:03]So, that makes this one. This is three and four.

[00:24:09]Which means this is two. This is nine here.

[00:24:12]Next to seven and eight. That 7 8 pair eliminates 7 8 in the rest of the box.

[00:24:18]This can't be seven or eight. It's six.

[00:24:20]This can't be 6 7 or 8. It's five, which makes that four.

[00:24:25]No five or six here. It's 7 8 as a pair.

[00:24:27]Three and four eliminate three and four in the rest of the row.

[00:24:31]This one eliminates one in the rest of the Sorry, one three or four in the rest of the box. This is 2 5 6.

[00:24:38]No two five here. No six here. No four here. This is 1 3 as a pair here.

[00:24:47]Four eliminates four in the rest of the column. Three eliminates three here.

[00:24:52]Where is three then in row eight? It has to be here. So, this is three, which means this is greater than three. This is greater than that, so it has to be 6 7. This is greater than that, so it must be 7 8.

[00:25:06]>> [snorts] [cough] >> We have a 6 7 8 triplet in column eight, which eliminates 6 7 8 in the rest of the column, so no six here. It's five.

[00:25:15]No 5 6 7 8 here. It's four.

[00:25:18]Four eliminates four here. So, it's five.

[00:25:22]No four in this row.

[00:25:25]That means where is the four in box nine? It has to be one It has to be here specifically. That makes this three, which makes that four. Three eliminates three here, so it's one and three.

[00:25:37]No fives here again.

[00:25:41]One eliminates one in the rest of the column. Where is one in row six then? It has to be here. So, that's one, which eliminates one in the rest of the box.

[00:25:51]Two eliminates two here, so it's one.

[00:25:54]So, no one, no one, no one.

[00:25:58]Two cannot be either of these.

[00:26:01]Um we have a hm.

[00:26:07]No one available here.

[00:26:10]No five available here because of five in the column.

[00:26:15]Six eliminates six in the rest of the box.

[00:26:21]Where is Six eliminates six in the rest of the column.

[00:26:28]Five eliminates five here.

[00:26:32]Where is eight in row seven? It has to be here. So, this is eight This is eight here, which makes this nine.

[00:26:41]It can't be eight or nine. It's seven.

[00:26:43]Which makes this eight, which makes that nine. Eight eliminates eight here, so it's seven. This can't be 7 8 or 9. It's two, which forces this to be eight.

[00:26:51]Therefore, this becomes a 1 6 pair here.

[00:27:00]Um remaining digits of box eight are 1 2 5 6 7 8.

[00:27:07]No one here.

[00:27:10]No eight here because of eight in the row.

[00:27:18]Okay.

[00:27:20]No nine here, so this is a 5 8 pair in box five, which eliminates five and eight in the rest of the box. So, this can't be cannot be eight here.

[00:27:30]Eight eliminates eight here, so that's nine, which means this can't be nine here.

[00:27:40]Um we have a 6 7 pair actually in column five and in row four, which eliminates 6 7 in the rest of the column and row.

[00:27:50]This can't be seven. It's eight. This can't be six or seven. It's nine.

[00:27:56]Uh Eight eliminates eight in the rest of the row here.

[00:28:03]This 2 5 7 as a triplet.

[00:28:07]Okay.

[00:28:09]Um hm.

[00:28:20]Whatever this digit is is the same as that digit there.

[00:28:26]Because those are 6 7 as a pair.

[00:28:33]Hm hm.

[00:28:51]Five eliminates five here, so that's six, which makes this seven, which makes that six, which makes that seven. That makes this eight and seven there. Eight eliminates eight here, so it's five and eight.

[00:29:02]Six eliminates six here. This is 2 7 as a pair, which eliminates 2 7 in the rest of the row. This can't be 2 7 because of the 2 7 pair, so it's one, which makes that two, which makes that seven, which makes that six. Seven eliminates seven here, so it's two.

[00:29:17]Two and seven eliminate two and seven here, so it's five and seven there.

[00:29:22]Two eliminates two here, so it's eight and two. Eight eliminates eight here, so it's seven and eight.

[00:29:29]Six eliminates six here, so it's two and six.

[00:29:33]This then has to be a 1 2 pair here, and this can't be two because of two in the row, so this is one. That's two.

[00:29:39]This can't be 2 6 or 7. It's five. Six eliminates six here, so it's one and six.

[00:29:47]>> [snorts] >> Um that was a little bit more difficult than easy, I think. But, is it significant enough that I would consider it challenging?

[00:29:59]Probably not.

[00:30:02]But, yeah, execution-wise, I felt that that was actually decently difficult or yeah, potentially challenging level.

[00:30:15]But, the logic wasn't hard.

[00:30:18]It was pretty It wasn't challenging level.

[00:30:21]Yeah, I don't know. I'm not sure if I would consider this easy or challenging.

[00:30:26]Um I don't know. What do you guys think?

[00:30:32]Let me know in the comments if you guys think this was easy or challenging, and I'll see you next time on Frank Puzzles.

[00:30:39]Take care.