# Can you solve it? 24 hour puzzle people

Logic problems to keep you up all night

The little-known sport of extreme puzzling held its premier tournament this weekend in Hungary. The annual 24 Hour Puzzle Championship is a physical and intellectual endurance event in which contestants from around the world solve puzzles non-stop from 10am on Saturday to 10am on Sunday.

“I have no idea why puzzlers from all over the world like this crazy championship,” said Gyorgy Istvan, one of this year’s organisers. “But it’s been going for 19 years. I guess it is because in each sport the top players like to test their skills in extreme ways.”

Nikola Zivanovic from Serbia came first this year out of a field of 32 contestants from 14 different countries. Neil Zussman from the UK was runner-up.

Today’s four puzzles are taken from the championship’s archive. I hope they give you a flavour of the kind of problems attempted at elite puzzle tournaments.

The first two are Masyu, a classic grid logic puzzle that originated in Japan. The third and fourth are variations: Arrow Masyu and Masyu Or Not. Since these puzzles are best solved with a pencil, I have put them on a pdf which you can print out here. Here’s the first Masyu puzzle:

The challenge in Masyu is to draw a single loop that goes through each black and white circle such that

* The loop goes through every white circle, and in at least one cell either just before or just after that white circle, the loop must turn 90 degrees

*The loop must turn 90 degrees at each black circle and go straight through the cells either side of that black circle.

Before we get to the other puzzles, here’s a tutorial on how to solve Masyu. Once you have internalised the rules, the images are self-explanatory.

A. This is the opening grid, with just black and white circles and no fragments of the loop.

B. Look at the white circle on the bottom row. The loop must go through every white circle, which it can do either horizontally or vertically. Here it can only go horizontally, since if it went vertically it would leave the grid, which is forbidden. Now look at the black circle on the right of the top row. There is only one way for the loop to turn 90 degrees at that circle and pass through one cell ether side, which is the way marked.

C. We can continue the loop through the other black circle on the top row. It has to proceed at a 90 degree angle, and there is only one way it can go and stay on the grid. Once we extend the line beyond the cell underneath it, it enters a cell with a white circle, and thus must carry on vertically through. On the bottom line, there is only one possible way the loop can make a 90 degree turn at the black circle, so we add that L, which joins up with the fragment through the white circle. The rule about white circles states that at least one cell at either side of the white circle the loop must make a 90 degree turn. It hasn’t done so on the left of the white circle, so it must do so on the right.

D Look at row 4, column 2. The fragment there has three possible ways to continue. We can, however, eliminate turning left or moving up, since this would create a fragment that could never link up to another fragment to close the loop. So we have to move to the right and join the descending fragment in column 3. The loop therefore must go vertically through the remaining white circle, and once it does there is only one way left to join the ends.

The Masyu puzzle I posted before the tutorial is considered ‘easy’, and would be solved by the top solvers in around 1min 15secs. This next one is also ‘easy’, and would be solved in about 1min 30secs.

If you are familiar with Masyu, you will enjoy the variations. In Arrow Masyu there are no circles on the grid. The challenge is to draw a Masyu loop through circles that you will draw on the grid. Every cell that can have a black or white circle in it must have a black or white circle in it. The loop may not pass through the greyed-out cells. Arrows in a cell indicate the number of Masyu circles that appear in that direction, up until the edge of the grid. (This example is considered medium, solvable by the top solvers in around 3mins 45secs.)

Masyu Or Not is the same as Masyu but with extra rules. Some cells are grey with a thick border. The loop may not pass through these greyed-out cells. Grey circles must also be passed through by the loop, but may not behave like black or white circles. (This example is considered hard, solvable by the best in 6mins 15secs.)

Here’s another link to the printable page with all four puzzles.

If you like this type of puzzle, and you fancy spending a 24 hours solving them in a competitive environment, I know just who you can call!

I’ll be back with the solutions at 5pm UK time.

I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me. Thanks to the team at the 24HPC for helping me with this week’s puzzles.

If you like Masyu (or want some simpler ones to practice), I include several in Puzzle Ninja, my book about Japanese logic puzzles.

Finally, I’d like to mention the inaugural Football School/Guardian Young Sportswriter of the Year competition. It’s for children aged 7-12. The prize is a trip to a Premier League game and your story published by the Guardian. For more details click here. The last date for entries is May 19.

Alex Bellos

The Guardian

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