sorted and shifted array

Discussion in 'C++' started by Vols, Jun 1, 2008.

1. VolsGuest

if you have a sorted and shifted array such like {5,6,7,1,2,3,4}, how
to find one element "2"?

Thanks.
Vol

Vols, Jun 1, 2008

2. Eric PruneauGuest

"Vols" <> a écrit dans le message de news:
...
>
> if you have a sorted and shifted array such like {5,6,7,1,2,3,4}, how
> to find one element "2"?
>
> Thanks.
> Vol

Check out algorithms like

std::find, std::find_if

int arr[5] = {1,2,3,4,5}
int* it = std::find(arr, arr+5, 2); // it now point to arr[1]

and you can use std::distance to obtain the position of the element

Eric Pruneau, Jun 1, 2008

3. Guest

On Jun 1, 11:03 am, Vols <> wrote:
>
> if you have a sorted and shifted array  such like {5,6,7,1,2,3,4}, how
> to find one element "2"?
>
> Thanks.
> Vol

the sorted and shifted array contains 2 sorted subsequence
first, find the 2 subsequence
then check which subsequence is the element in, and do binary search

, Jun 2, 2008
4. Jim LangstonGuest

Vols wrote:
>
> if you have a sorted and shifted array such like {5,6,7,1,2,3,4}, how
> to find one element "2"?

Your requirements are not clear. Do you need to find the element that
contains the value 2, or the element that was orignally the 2nd element
before the shift?

--
Jim Langston

Jim Langston, Jun 2, 2008
5. SzeGuest

On 1 Jun., 05:03, Vols <> wrote:
>
> if you have a sorted and shifted array such like {5,6,7,1,2,3,4}, how
> to find one element "2"?

If you meant that every unshifted sequence, you want to search through
has
in general the form {1,2,3,4,...,n}|n = amount of elements

You could easily calculate about how many elements it is shifted,
through:
shiftingRange = n - (firstValue - 1)
this algorithm would return 7 if firstValue is 1, which is the same
sequence
because it`s a full shift, but 0 would be nicer, to get this you could
do this:
shiftingRange = (n - (firstValue - 1))%n
So you would get the index of the value you are searching for with
find(x) = (shiftingRange + x - 1) % 7 // -1 to make it a c++ array
index, which starts by zero

find(2) = ((7 - (5 - 1))%7 + 2 - 1) % 7 = 4 // with your sequence as
example
find(5) = (3 + 5 - 1) % 7 = 0

My answer is just a guess of what you could have meant,
you should represent what do you want to achieve.

Sze, Jun 2, 2008