Re: [algogeeks] Number Theory (Power of 3 )

2011-12-09 Thread Gaurav Kumar
What if we create a base 3 number from the given number N and then check if 
there is only 1 bit with value 1 and all values should be 0. For example, if 
lets say the number is 27. Its base 3 number will be 1 0 0 0, now since there 
is only 1 single 1 present in this representation, it is a power of 3.

Gaurav

On Dec 7, 2011, at 6:03 PM, saurabh singh wrote:

 Originaly problem rules out the use of log.Moreover log (or any floating 
 point operations) take lot of hardware time as they are emulated on the 
 floating point environment on most machines.Thirdly precision problem for 
 higher values of n may cause your solution to give wron g answers,,,
 
 On Wed, Dec 7, 2011 at 11:54 PM, tech coder techcoderonw...@gmail.com wrote:
 what about this   log(base 3 n)  is of  integral type then n is a power of 3
 
 
 On Mon, Dec 5, 2011 at 11:36 PM, Dave dave_and_da...@juno.com wrote:
 @Carl: You can generate the constants the first time the procedure is
 called. There is no need to do them every time. So the first call
 would be O(wordsize) but subsequent calls are O(1).
 
 Dave
 
 On Dec 5, 10:28 am, Carl Barton odysseus.ulys...@gmail.com wrote:
  Sorry, I was being a bit vague. I meant what would the time complexity be
  then?
  As I understand your Constant time is Dependant on the constant pre
  computation you do, which is no longer the case when you generalise
 
  On 5 December 2011 16:14, Dave dave_and_da...@juno.com wrote:
 
 
 
   @Carl: Of course. For any given word size, extend the tables of powers
   of 2 and of 3 and change the for loop limit.
 
   Dave
 
   On Dec 5, 9:36 am, Carl Barton odysseus.ulys...@gmail.com wrote:
Ah I see, in which case could you not generalise your solution for all
integers?
By taking into account the size of words on the computer for example?
 
On 5 December 2011 15:09, Dave dave_and_da...@juno.com wrote:
 
 @Carl: Yes, as coded, my algorithm is for 32-bit integers. But the
 original poster asked for a solution using bit manipulation, and
 modulus and division are arithmetic operations, not bit operations.
 
 Dave
 
 On Dec 5, 8:56 am, Carl Barton odysseus.ulys...@gmail.com wrote:
  @Dave Yours only works for a certain subset of all possible powers
   or 3
  doesn't it? So WgpShashank's would be more general?
 
  On 5 December 2011 14:30, Dave dave_and_da...@juno.com wrote:
 
   @WgpShashank: Yours is an O(log n) solution. Mine is O(1).
 
   Dave
 
   On Dec 5, 6:21 am, WgpShashank shashank7andr...@gmail.com wrote:
@SAMMM  have a look
 
* *solution is to keep dividing the number by 3, i.e, do n = n/3
iteratively. In any iteration, if n%3 becomes non-zero and n is
   not 1
   then
n is not a power of 3, otherwise n is a power of 3
 
check it out ?http://codepad.org/863ptoBE
 
Thanks
Shashank
Computer Science
BIT Mesrahttp://
  www.facebook.com/wgpshashankhttp://shashank7s.blogspot.com/
 
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 Life is a Game. The more u play, the more u win, the more u win , the more 
 successfully u play
 
 
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Re: [algogeeks] Number theory

2011-08-16 Thread Nitin Nizhawan
I think 2^(n-1) - 1

On Tue, Aug 16, 2011 at 8:36 PM, sameer gupta gupta.sameer...@gmail.comwrote:

  no. of ways you can write a no. as sum of other non-zero positive
 integers
 like 3 can be written in
 3 ways:
 1+1+1,
 1+2
 2+1
  imp. 2+1 and 1+2 are different
 find the answer and give and prove formula for any value 'n'

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Re: [algogeeks] Number theory

2011-08-16 Thread Bharat Kul Ratan
It might be useful:
http://www.artofproblemsolving.com/Wiki/index.php/Partition_%28combinatorics%29

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