Author round-table 014

InterviewsAuthor round-table

Let's Shikaku!

The theme this time is Shikaku. Our guests are Guten and Ryohei Nakai. From Nikoli we have NyanBaz and Nob.

NyanBazShikaku is an old puzzle born in 1989. Shikaku lost popularity along the way and seemed to have disappeared. It started to appear on nikoli.com and regained its energy after that. What is its charm?

GutenIt's easy to understand how to do it. There are no other puzzles with rules as plain as that elsewhere.

NobI agree.

NyanBazHow do you think Ryohei?

Ryohei NakaiYou can be careful and go ahead by advancing little by little or strike out and decide boldly, both are ways to solve it. The bold ways appeared in nikoli.com, and Shikaku evolved with that. I solved an old Shikaku Pencil Puzzle Book recently, but it was very very different.

NobThere were no Shikaku with the rough bold system in the old days.

NyanBazMaybe they didn't use big numbers then?

NobSure, but problems with big numbers still lets you do it step by step, the fine (small block) way.

NyanBazThat's where you go ahead and expand it with temporarily set blocks little by little. That was the standard with old hard problems.

Ryohei NakaiThat's of course interesting but...

GutenNow that Shikaku has become popular again in nikoli.com, would the wild guessing ways be liked better than that fine tiptoeing system?

NobMaybe yes. It's a pleasant feeling when it is solved at a burst.

Ryohei NakaiThat seems to be how aspirin's problems go.

GutenWhat? Is it that dynamic? There are many places where progress goes through just one number you have to put in a specific cell like it happens with his problems.

NobHis problems are really not easy even when there are so few numbers in a puzzle.

Ryohei NakaiHis problems are made really carefully so I am not sure if they are that dynamic. I like them. But I don't plan to imitate it.

NobHis problems have a strong influence on other authors. Akasyo's problems with only a few numbers may have been an influence for Aspirin.

GutenSure. But I don't want to solve a lot of puzzles like that. It's not good when there are only such problems. It may be enough that only Aspirin makes problems like that.

NobWe welcome Shikaku problems that have only small numbers such as 2, 3, or 4. We want to offer different types of problems.

GutenMy ideal is to incorporate both the fine system stuff together with the coarser large numbers in one problem. That will remain my personal ideal to the last.

NobThere weren't a lot of problems that you began by putting in big numbers in the old days.

NyanBazRyohei's Shikaku problem selected for the pick of the puzzles recently had an 18 to fit first. (Deadline Nov 2010, Medium)

Ryohei NakaiI may have been the first to make a problem where you have to start from a big number.

NyanBazWhy did you do it that way then?

Ryohei NakaiHmmm, I don't really remember why.

GutenYou'd do it automatically if you intend to make a big easy problem.

NobWhen you make Shikaku, do you think about where to start the solution form?

GutenYes, with Shikaku the first thing I settle is where the start goes.

Ryohei NakaiI set the entry like that, too.

GutenThen, where to put the numbers are often decided by that.

Ryohei NakaiI place all of the numbers first as well as where the entry goes.

GutenI don't decide the placement from the beginning.

NyanBazYou make a lot of problems with an attractive looking placement. Does that all happen as you go along?

GutenLike I said a little while back, with the entry point set first some of the placement becomes fixed there. Then I put numbers making use of what grows out of that, how the entry was placed. I pick the better looking placement if I seem able to do that. But appearance often emerges just going along.

NyanBazPersonal inclination is what determines the number placement with Shikaku.

Ryohei NakaiI like numbers lined up diagonally. I feel that makes it easier to arrange. However, there is the little problem that it makes for more one-cell width boxes.

GutenWhen it's diagonal placement, I place the numbers thinking about the connection with what has to be set temporarily. With a square the direction it can spread is limited to length and breadth placements, and I extend that little by little.

NyanBazAhaaaa.

GutenI make it as easy as possible to solve when there are few numbers to go by.

Ryohei NakaiWhen placing just few numbers it is bound to become harder.

GutenJust at a glance it looks like there is no way in. To avoid that I make an effort so it doesn't become as hard as all that. In fact, not putting a number in the corners of the board needs courage.

Ryohei NakaiIf I don't set a number in the corners, it is usually easy to find the number to reach that cell. I see to it that such a problem cannot be solved by that method.

GutenThinking that deeply is too much for me. So I put numbers in the corner. (laughs)

NyanBazIsn't it scary when the method where only one number will reach a cell can be used in a part you did not aim at?

GutenSure, it is just that. My first rule is to see that it will not work that way.

Ryohei NakaiMe too. But, it's impossible to completely prevent it.

GutenWhen it is impossible to avoid, I make sure that part can be decided as soon as possible. Or I make it so there is a dent. With a dent it is easy to see that only some specific number will reach that. However, I can't always guard against everything.

NobThat is a weak point with Shikaku.

GutenBut there are few problems where you can escape from this way ahead. And then there are many problems that are solved quickly if you use this method.

NobThat just about says it.

GutenThere are two ways of thinking among authors. It seems to me that half are trying to evade this method, and half trust the solvers to sort it out.

Ryohei NakaiThere are authors who try to make it so it is used actively. For example, nyoroppyi.

NobIt isn't a bad thing in hard problems.

Ryohei NakaiBut I want to use it at a corner, an edge, or in a dent. Where there are no other numbers or a wall around it, it won't be noticed.

GutenI can make very hard Shikaku. For example, I narrow it down to how to cut a box in two ways. When I go this way no number can reach the remaining cell. So the other way will be right. Letting in such methods, endlessly, will make it hard. However, authors individually put a limit on that. So that prevents it going too far.

NobThere was a time when that sort of method was how problems got solved.

NyanBazThat may be why Shikaku became dull then.

GutenWhen I try to solve it on paper, setting things temporarily is troublesome. That way it's comfortable to solve on a PC however. There are more problems that can be solved smoothly on a PC. That was reflected back in how it can be done on paper.

NobProblems that are solved smoothly are interesting even if I solve them on paper. That's why the popularity revived.

Ryohei NakaiIt is troublesome to count the number of cells on paper. So I feel paper hard to use with the big numbers.

GutenI rather like counting cells.

Ryohei NakaiI don't want to make errors in counting. I lose heart when I count wrong and get disappointed.

NyanBazPlease let us hear your opinions about numbers.

GutenI want an even number to be in the 1xN boxes.

Ryohei NakaiLike for example with 22, I want it to be a 1x22 box. When we are talking about large problems.

GutenIf I were to use 24 I would want put a 24 in two places and make one of them 1x24.

Ryohei NakaiYou have made a problem where four 36s formed the center.

NyanBazThe numbers are the same but the shape of the boxes were different.

GutenSure. I want to put unexpected shapes. Then also, I want someone used to puzzles to think they know what is coming rather than be prepared for something unexpected.

NobJust like in a horror movie. The monster gradually approaches. You don't want it to come. But if a monster appears, you are pleased.

GutenAt first I wanted to make a problem that wouldn't work if you were trying to solve it with wild guesses, illogically. With 12 you first think of 2x6 and 3x4 intuitively. So I thought to use 1x12.

NobDo you think like that about numbers Ryohei?

Ryohei NakaiI'm not particular about numbers. I consider the place to put the number. I like fitting in the boxes from the corner. If the same method is repeated in that section, it's absolutely more obvious at a corner than at the center.

NobYou give priority to make it easy to decide exactly how a box goes.

Ryohei NakaiI style myself as an easy author. So that's a natural. (laughs)

NobYou make a lot of hard problems recently. You look like becoming a hard author.

NyanBazWhat is the number you like best?

Ryohei NakaiIt's 12. 12, 18, and 24.

NobThey are numbers with many divisors. A reasonable preference.

Ryohei NakaiI like it when it develops in a straightforward manner, even with the many divisors. It has the element of surprise.

GutenDon't you think you are losing something? When there are so many ways to shape it.

Ryohei NakaiWell, that's how an easy author feels.

GutenYou do it just like you say, amazing.

NobThat's the Ryohei style.

NyanBazWhat is the number you like best Guten?

GutenI like 16.

NyanBazThere are three ways with that 4x4, 2x8, and 1x16.

GutenI like to make it a square. The square or 2x8. 1x16 is sometimes good for variety. I really want to use 25. But it becomes dull even if I think of some way to fit it in.

Ryohei NakaiI don't like prime numbers. I want to use prime numbers only up to 7. They let you give so few patterns to the boxes.

GutenI like numbers with only a few shapes for the boxes. How do you think about 2?

Ryohei NakaiWhen I make a problem with only large numbers, then if I end up having to use a 2, I feel like a loser. (laughs)

GutenI can understand that. Would you use 2 to some good effect?

Ryohei NakaiNo. Is there any good method for using 2?

GutenYes, there is. When there are a lot of 2s, knowing that they can extend in two directions. Then, when one is the sure way ahead, all is decided.

NobThat's cool.

NyanBazIt's interesting that your personality is reflected on the preference for numbers. Then here comes the last question. What is some advice to people who are weak at Shikaku?

Ryohei NakaiI think it'll become interesting when you learn to set boxes temporarily, trying out things.

GutenI hear that a lot of people solve Shikaku with wild guesses. If that is fun then do it by all means. But after solving by wild guessing, please go back and try to solve it by logic. That way you will understand another way to enjoy Shikaku.

NyanBazThank you for today.


Discussion on Dec 2010 Published on Dec 26, 2013

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