## Sudoku Xtra 24

Feb 9th

*Sudoku Xtra 24* is now finally available! It’s packed with 130 puzzles of a wide range of types, including a huge variety of sudoku variants.

This issue I’ve included some new sudoku types such as **Two-grid Interconnected Sudoku, Mystery Multiple Sudoku** and** Blackout Sudok**u. I’ve also made an effort to include all of the most popular variants as requested by readers, such as **Consecutive Sudoku, Inequality Sudoku, Odd/Even Sudoku** – and of course many more.

There’s also a range of non-sudoku puzzles, including **Light-up/Akari, Hashi, Slitherlink, Battleships, Skyscrapers, Calcudoku, Futoshiki, No Four in a Row**, and more!

It’s available either as a PDF to print yourself (every page is self-contained, so you can print only the pages you want), or as a professionally-printed book direct from Amazon – there are links for all of these on the Sudoku Xtra site.

## Sum Skyscraper

Jan 17th

Sum-Skyscraper 5×5 puzzleI made this puzzle just before Christmas, and it’s been waiting on my desktop to be posted here ever since! Well, now it finally has been.

This is a Sum Skyscraper. Place the digits 1 to 5 once each into every row and column in the grid. Numbers *outside *the grid provide the **total** (i.e. sum) of ‘visible’ grid digits along that row or column, if you imagine each digit as a building of that many storeys. Taller buildings always obscure shorter ones. So, for example, a clue for 21354 from the top of such a column would be 10, since the 2, 3 and 5 are visible (the 1 and 4 are obscured by the 2 and 5 respectively), and 2+3+5 = 10.

## Christmas Star Sudoku

Dec 21st

Sudoku Christmas Star puzzleA Sudoku, in a star shape.

Just that. (Place 1-9 once each into every row, column and bold-lined 3×3 box).

## Bridge Mazes

Nov 6th

Weaved Bridge Maze 2

Weaved Bridge Maze 1

I’ve recently been making some material for a book of kids’ mazes, and so I thought it would be fun to post a harder version of some of those puzzles here.

First-up, here’s a weave maze, so-called because the paths weave over and under each other. In this puzzle I’ve drawn narrow bridges where one path crosses over another.

If the first one is too easy for you, try the second! It needs to be printed full-page in order to have enough space to solve it.

Just **enter at the top of the maze** and follow paths until you exit at the bottom of the maze.

## Wraparound Numberlink

Sep 25th

I’m currently working on a forthcoming book (*The Mammoth Book of Brain Workouts*, published next year in the UK by Constable & Robinson, and in the US by Running Press), and have been experimenting with something I wrote about briefly a few years ago but hadn’t really tried since – variants on Numberlink.

Numberlink puzzles have proved popular recently in various guises, including *Flow Free* and other apps on mobile devices such as the iPhone. There are quite a few such apps available, but none of them force a unique solution on the user (and generally the puzzles do indeed have many different solutions), which when you’re playing against a computer that grades you isn’t necessarily a problem since you can at least be marked correct/wrong automatically.

For a logic puzzle solver, such vague puzzles are perhaps a bit disappointing because you will reach a point during solving where you can’t eliminate any options because they may all be valid, despite being contradictory.

I’ve made a printed book of 200 of these Flow Free puzzles – you can get it from Amazon.com (currently $5.36) or Amazon.co.uk (£3.95) – and they’re actually quite fun to solve despite the multiple solutions (not all the puzzles have multiple solutions, but some do). Unlike traditional Numberlink the puzzles include an explicit rule that every cell in the grid must be used, which eliminates a lot of potential solutions and means the puzzles usually require some thought.

Toroidal numberlink 6×6 puzzle

Toroidal numberlink 5×5 puzzle

But such multi-solution puzzles are not the kind of puzzle I usually post, so I’m going to stick to logic puzzles with unique solutions on this blog.

It turns out that if you allow lines on a Numberlink puzzle to wrap around one edge and come back on the other – so if a line goes off one end of a row or column it comes back on at the other end of the same row or column – that the puzzles get very difficult very quickly. In fact, even at 5×5 many such puzzles are very challenging. Once you get to 6×6, I have real trouble with them.

Here’s a 5×5 and a 6×6 puzzle for you to try. Let me know how you get on! There’s no explicit rule that every cell must be used – but as a hint I can tell you that they are anyway. There’s a unique solution to each puzzle.

## 101 Giant Sudoku series

Jul 29th

I’ve recently launched a new series of ‘101 Giant Sudoku’ books, to cater for those who like their Sudoku to be considerably larger than normal!

You can see the entire series at PuzzleBooks.org (scroll to the bottom) or visit Amazon and search for “101 giant sudoku”.

There are currently 12 books in the series: 14×14, 15×15, 16×16, 18×18, 20×20, 21×21, 22×22, 24×24, 25×25, 28×28, 30×30 and 36×36.

The larger puzzles work just as you’d expected, so in Sudoku 36×36, for example, you must place 0-9 and A-Z into every one of the 36 rows, 36 columns and 36 6×6 boxes!

These puzzles are designed so they don’t need any advanced logic – just scan the rows and columns and boxes to see what’s missing and what can fit where.

All of the puzzles are designed with attractive 8-way symmetry patterns.

## Sum Skyscraper puzzles

May 14th

Following-up yesterday’s Skyscraper puzzles, I thought I’d post a couple of Sum Skyscraper variant puzzles.

Sum Skyscraper puzzles are very similar to Skyscraper puzzles, so no number can repeat in any row or column and external ’skyscraper’ clues reveal information about the numbers in the main grid. In 5×5 puzzles place 1-5, and in 6×6 puzzles place 1-6.

Each number in the completed grid represents a building of that many storeys, and place the buildings in such a way that each given number outside the grid represents the *sum of the number of buildings* that can be seen from that point, looking only at that number’s row or column. A building with a higher value always obscures a building with a lower value, while a building with a lower value never obscures a building with a higher value. So the clue ‘6′ in a 5×5 puzzle would indicate that the buildings ‘1′ and ‘5′ can be seen (’5′ is always visible in 5×5 puzzles), so the solution to a row might be 15234.

## Skyscraper puzzles

May 13th

I haven’t posted here for a while, but to celebrate the advent of reduced-clue skyscraper puzzles on PuzzleMix.com earlier today I thought I’d post a few Skyscraper puzzles here.

Skyscraper puzzles combine the no-repeat row and column constraints of sudoku with novel additional clues. In these 5×5 puzzles, place the numbers 1-5 once each into every row and column. Each number in the completed grid represents a building of that many storeys.

Place the buildings in such a way that each given number outside the grid represents the number of buildings that can be seen from that point, looking only at that number’s row or column. A building with a higher value always obscures a building with a lower value, while a building with a lower value never obscures a building with a higher value.

## Sudoku Xtra 21

Oct 29th

*Sudoku Xtra 21* is now available, both as a PDF download to print yourself and also as a pre-printed book from your local Amazon store. Follow the links on the Sudoku Xtra website to get hold of it in your preferred form.

Sudoku Xtra 21 is packed full of 144 top-quality logic puzzles covering a wide range of types. There is a particular emphasis on Sudoku and new varieties appearing for the first time in this volume include **Quad-Max Sudoku, Anti-Knight Sudoku, Slashed Sudoku, Minus Little Killer, Product Frame Sudoku, Headless Worm Sudoku, Extra Region Windmill Sudoku, Non-Consecutive Diagonal Sudoku, Mystery Calcudoku Zero** and a giant **Trio 13-grid Samurai Sudoku**.

The very first page features a large **Arrow Samurai Sudoku**, and other returning variants that were recently introduced to the series include **Worm Sudoku, Quad Clue Sudoku, Offset Sudoku, Sudoku XV** and **Kropki Sudoku**.

Not only that, but there’s **Hanjie, Futoshiki, Hashi, Yajilin, Calcudoku, Dominoes, Hitori, Slitherlink** and many more logic puzzles.

Pre-printed copies are on top-quality, 8.5×11 inch paper ideal for solving on, while download PDFs are designed to fit both A4 and Letter paper for printing.

## iPad, iPhone and other touch support on PuzzleMix

Sep 28th

Just a quick heads-up that PuzzleMix, my site where you can play a wide range of puzzles online, now supports touch screen play for all of the number entry puzzles – so that’s Sudoku, Killer Sudoku, Futoshiki, Calcudoku, Skyscraper, Sudoku X, Kropki Sudoku, Killer Sudoku Pro, Jigsaw Sudoku, Consecutive Sudoku, Wraparound Sudoku, Sudoku XV, Killer Sudoku X, Odd Pair Sudoku and more.

It’s pretty darn awesome, even if I do say so myself! It handles the screen touch events directly so it’s just as fast as running a native application on the iPad or iPhone. It also works on other devices.

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