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### 967 - Circular

Posted: **Fri Nov 03, 2006 10:20 am**

by **sohel**

Seems it is the first post of this problem.

Circular
Isn't it true that all the valid numbers consist only the digits {1, 3, 5, 7}.

I basically generated all the numbers in the range [100, 1000000) using recursion and checked the validity. But I am getting WA.

**Input: 100 999999**
**Output: 42 Circular Primes.**
Is it correct?

Posted: **Fri Nov 03, 2006 10:30 am**

by **stubbscroll**

Your answer is correct, but there are many valid numbers containing 9 (and none containing 5).

Did you remember to output Prime without an ending s when the answer is one? It's the only trap I can think of.

### oooppsss

Posted: **Fri Nov 03, 2006 10:34 am**

by **sohel**

ooopss..

I meant to write { 1, 3, 7, 9}.. and not {1, 3, 5, 7}

any other ideas?

[Edit]: got accepted.... made a stupid/silly mistake in printing.

Posted: **Fri Nov 03, 2006 11:51 pm**

by **mpi**

i'm following the same approach than you and i always get TLE. After generating all circular primes between 100..1000000, i only have to do a simple iteration through my array and count the 1's. It's simple, but however i get TLE.

Posted: **Sat Nov 04, 2006 12:14 am**

by **rio**

mpi wrote:i only have to do a simple iteration through my array and count the 1's.

This approach is too slow. Think about it. (there are just fourty few cir-primes)

Posted: **Sat Nov 04, 2006 12:53 am**

by **mpi**

You are right. There are only 42 numbers. What i was thinking about?

Now i get AC in 0.674s.

Thanks

Posted: **Thu Nov 09, 2006 10:59 pm**

by **farzane**

could someone please help me and tell me what's wrong with this code?

I'm getting WA.It is an easy problem I think so.

Posted: **Fri Nov 10, 2006 6:22 am**

by **rio**

cir[9] = 917, but its not a prime.So check why this number pass your Circular prime test.

Posted: **Fri Nov 10, 2006 1:13 pm**

by **farzane**

Thank you very much rio.I found my mistake ang got AC.

Posted: **Wed Mar 07, 2007 10:20 am**

by **Rupak**

I think i can't understand the problem statements .

For 917 we should check the numbers 917, 179 and 791 .

Here 917 isn't prime, 179 is prime and also 791 isn't prime .

So can we call the number 917 be a circular prime ?

Posted: **Wed Mar 07, 2007 10:30 am**

by **helloneo**

No, 917 is not a circular prime.. because 917 and 791 is not a prime as you said..

Posted: **Fri Jun 01, 2007 6:06 pm**

by **sumantbhardvaj**

Somebody plz provide me some test case.. I m constantly getting wrong answer for this problem..thanx in advance

Posted: **Fri Jun 01, 2007 6:39 pm**

by **little joey**

I don't think there are any special cases. If you find 42 circular primes between 100 and 1000000, as mentioned above, you have a very good chance that your program is right. Your only worry then is to get the output format right. Have you carefully checked your output for the sample input?

Posted: **Fri Jun 01, 2007 6:43 pm**

by **sumantbhardvaj**

yeah ! you are absolutely right. I was not printing correctly when we have output 1. later on i found the mistake and got AC

.why do acm problems have such irrelevant output formats.. i nearly wasted 1 hr for that.

Posted: **Sat Jul 28, 2007 5:12 pm**

by **hamedv**

i got wa.

what's wrong with my code???