# need help defining Constant memory requirement

Jani Yusef jani at persian.com
Sun Sep 19 23:28:35 CEST 2004

```Heiko Wundram <heikowu at ceosg.de> wrote in message news:<mailman.3507.1095603871.5135.python-list at python.org>...
> Am Sonntag, 19. September 2004 07:00 schrieben Sie:
> > I am sure the solution is O(n) since the list must
> > only iterated once and the dictionary is O(1), correct?
> > Thanks for the help!!
>
> In case you haven't found a solution yet, think about the properties of the
> sum of the numbers of the sequence which is n*(n-1)/2 + x with 0 < x < n,
> where finding out why this equation holds and what x is is up to you.
>
> (n being defined as in your example, a sequence having n elements with the
> elements in 1..n-1 and only one repeated)
>
> Heiko.

Got it!! Thanks for your help.
Here is my revised and working code
i=[1,2,3,4,5,6,3]
s0=len(i)*(len(i)+1)/2
s1=0
for a in i:
sum1+=a
return (sum1-sum0)%len(i)
I think my main malfunction was with thinking that this was mor
ecomplex tna it was. By refocusing on the simple problem statement as
suggested the solution came easier. Thanks again.

```