[CHALLENGE] Power Of Two

Question

The challenge is quite simple ... You'll have to do a function that tells whether or not a number (the input) is a power of two.

But beware ! Two criteria will be judged as the challenge is easy in itself. Your function will have to be AS OPTIMIZED AS POSSIBLE and AS SHORT AS POSSIBLE.

Good luck :)

Answer 1

x & (x - 1) == 0

Answer 2

My answer:

https://code.sololearn.com/cCmfg7Z5Kqey/?ref=app

Answer 3

@sayan, a number of two is binary written as looots of 0s, and one and only one number 1, wherever in the number.
So if you reduce it by 1, it will have no common bits with its past self
Examples :
8 : 1000 & 0111 = 0000
7 : 0111 & 0110 = 0110
6 : 0110 & 0101 = 0100

@Roman, reaaaaally nice !

Answer 4

here you go! hope you like it!
https://code.sololearn.com/cocQa8N0gEG7/#cpp

Answer 5

hows this

https://code.sololearn.com/cJV22kgRfg3W/?ref=app

Answer 6

@sayan, nice but log is expensive

Answer 7

@sayan i like your idea in version 2 👍👍👍

Answer 8

baptiste
please explain that & thing up there .
idk that

Answer 9

It's "and" bitwise operation. All numbers that are powers of two has only one 1 bit. & (x - 1) remove this bit, so result will be 0.

Answer 10

version 2
no log
no imporing

https://code.sololearn.com/cAvL7fCAob5R/?ref=app

Answer 11

x-1 and & are single instructions at machine level. floating log and int<>float conversion are 100x more expensive

Answer 12

https://code.sololearn.com/cbxAg0Yv6Dav/?ref=app i wish i knew the bitwise thing! not very optimized but here my try on this

Answer 13

@Baptiste Here is the answer for q^p for any q: http://cr.yp.to/papers/powers.pdf

Answer 14

if p&(p-1)==0 is the fastest way to see if p is a pure power of two

Answer 15

ooh...
ya but brother i did not know that thing
that binary operator...
baptiste yesterday explained me

Answer 16

vcc
baptiste
its my 4 th version
in python
it can calculate up to "3 lakh " yes
check it out
https://code.sololearn.com/cT5WxLWt9jIk/?ref=app

Answer 17

3 lakh ....
more more more

Answer 18

Good ! You can use integer div for k (//)

Answer 19

What is a lakh ?

Answer 20

3 lakh=300k