I had the same question . The example in the IB is not easy, considering you can have arrows of length 1 (but still have a unique solution).

Fred

I think I can answer this question:

Consider a such grid where you have more than one arrow from each circle. Then, if you remove one arrow from that circle, it's also a valid grid, but perhaps it has more than one solution considering the starting configuration. If so, the entire problem will have more than one solution. Rohan cannot ask us to add some additional arrows to avoid the fact that the grid has more than one solution...

Therefore the grid must have a unique solution with a unique arrow from each circle .

I don't know if I'm clear, it's a bit hard to explain in English...

Fred

Nice explanation, Fred. I think you are right. Something else I noticed in this puzzle. In the example the middle circles may collect the numbers in two possible ways. I don't know is this counts as unique or double solution. The numbers are surely unchanged but maybe it's not bad to know does the same case can appear in real puzzle.

Nikola

Edited by Nikola 2011-09-07 5:22 PM

Thanks, Fred. Everything is clear. And I noticed the same point as Nikola.

Regarding Symmetric Arrow Sudoku:

1. There is one unique arrow from each circle. This arrow must have a 180-degree symmetric arrow from the opposite circle. Fred's earlier post is absolutely correct.

2. There CAN be arrows of length one.

3. In the example, the middle circles can collect its numbers in two ways. The '9' can collect 4-5 and 5-4 (Similarly, the 1-3 and 3-1 for the '4'). But, the solution does not change and both ways is considered to be the SAME SOLUTION. As long as you collect the numbers from the same cells, the arrows are the same, irrespective of the order/direction.

4. No part of an arrow can go outside the grid. It can travel only through centres of neighbouring cells (in standard format), i.e. it can go in any of the 8 directions, but it cannot touch/cross the grid border.

5. I should've put a better example in the IB :-)

(I will create one more example of Symmetric Arrow Sudoku and post it by tomorrow, it should be clearer then)

Edited by Rohan Rao 2011-09-07 6:24 PM

For 0-9 Arrow Sudoku:

1. Can a circle have more than one arrow?
2. If so, can the sum change over the different arrows? Say, a circle has the digits 1 and 2 in it, can one arrow sum to 12 and the other sum to 21?

I was wondering this because the instructions says both orientations would be considered correct. And I would assume if the sum of each circle is unique, it would be more logical to just accept only the correct sum for the circle as an answer. My other idea for the reasoning would be that some circles have their digits given, but not necessarily in the right order and people might forget to change it when putting in the answer key.

0-9 Arrow Sudoku
--------------------
Each circle will have exactly one arrow.
Circles won't have givens, if that helps.

I think Rohan wanted to clarify that while entering the answer, one can enter the 2 digits in the circle in any order.

Each circle has exactly one arrow. That should solve the problem now. Of course, you will get a unique order of the two digits inside a circle while solving.

Both orientations are accepted as correct 'answers' just for convenience of players. As long as you get the two correct digits in the circle, it is ok for me. For example, an arrow over two cells may have 0 and 8 in its circle. The sum is obviously not 80. So, even if a player types '80' instead of '08' (maybe due to quickly typing it from the paper), it is as good as correct.

Here is a fairly easy Symmetric Arrow Sudoku that you can try out:





Solution:

If X submits 11 correct sudokus and 13 digits correct in the last sudoku, and one of the five wrong digits is a given clue. Does X get the time bonus ?

Edited by rakesh_rai 2011-09-09 4:22 PM

Yes, of course.

Password protected booklet uploaded. It has 12 pages, each page one Sudoku. There is no cover page.

nice set of SUDOS!!! (it was really CRAZY)
I dont know what happens to me while having sudoku test..
kinda find difficult to solve any sudoku..
Just missed submitting my sum1 sudoku answer.
but anyways it was nice experience
surely i need lots of practise to get command on sudoku.

Thanks for the puzzles Rohan

awesome puzzles Rohan......the arrows have really made me crazy!!!!

Thanks Swaroop, flk and Neeraj. A lot of people have gone crazy due to different reasons :-)

Excellent test, really had fun solving :) Unfortunately I made the awesomely horrible mistake of forgetting to click "submit answers" after half time :P But really enjoyed it. especially missing arrow Sudoku, which was quite confusing.. :P

Thanks a lot for a nice set of puzzles! :-)
I had a good time solving (a few) of them this morning. It was my first time.
During the test I had a few more solved, and was busy with another one when I noticed my time was almost over. Then I submitted already one answer and tried to finish the other one quickly, assuming I could submit (with penalty) after the time was over. I really only needed 10 more seconds. But I wasn't able to do so after the 110 minutes have passed.

Question: can you submit part of your answers first and later some more, when the time is not over yet?

Normally I am on the other side of the process; I do prepare sudokus for the Dutch and the German championships, and I am not very used to solving in a race against time. But I will participate more often in the future. Liked it a lot!

Yes, that is allowed and that is advisable.
It is always better to solve 2-3 puzzles, submit them and solve more.

Nice test Rohan. The intuitions I had by just looking at the grid ultimately proved to be true in some grids. Enjoyed all the sudokus (that I could solve). Already looking forward to "Crazier Arrows."

Edited by rakesh_rai 2011-09-11 3:58 PM

Thanks Prasanna, Richard, Rakesh.

It was an excellent set of puzzles. Thank you so much Rohan + admnistrators. Pity I wasted a lot of time to no avail on one of them (found the correct solution later).

Just a remark. I noticed the CLAIM BONUS button is dangerously close to the SUBMIT ANSWERS one, a couple of times I nearly hit it by mistake, better to move it a bit out of the way, at the end of the day it has to be used only once.....

With no one participating in Crazy Arrows now, the test is over. 3 players managed to solve more than 9 Sudokus and they take the podium - motris (11), Nikola(10), Kota(10). Congratulations to them and thank you everyone for participating.

Indian results : Rakesh, Amit and Jaipal take the top 3 spots.
Overall 184 players participated, and 134 got non-zero scores.

A tough test indeed with so many zero scores and many players not submitting anything towards the end. Although there were many easy puzzles, I thought SYMMETRIC was highly undervalued, thus trapping many solvers. It was only 75 points, but is solved by only 10 players. Having correct points for that puzzle would have been a huge step forward for a perfect test.

I can't comment on this test since I didn't finish, but on the last few tests I've caught that this button is not "active" until you have enough correctly formatted answers in the system. In other words, while it is there to click on, it cannot end your test until you could possible have a bonus to have. It also has a "are you sure" dialog afterwards which always costs me another minute of bonus as I keep forgetting it exists and losing 3 seconds to go over a quanta of minute.

I didn't post any comments during the test for a few reasons - first I was rushing off to help run a puzzle event and didn't have time and also I had some mixed feelings because the puzzles were great in places and hard in places and it really paid to switch to new puzzles. Some of it may be that puzzles like Symmetric Arrow were simply unfamiliar, but I also felt a puzzle like that had a lot of necessary steps at least under time pressure that felt more like guesses than deductions. So I put Symmetric quickly on my do not do pile until after I ran out of time. I ended up getting back to Sum 1 and Missing Arrow (worth more) before running out of time on Symmetric. Outside of those three puzzles, I think I really liked everything on the test. Thanks Rohan for a really creative set of arrow variations. I'm sure I'll be playing with some of these again in the future.