Hi,

I was wondering did anyone seen anything like this before and knows a solution to this problem ?

Problem:

Given an unsorted array of N numbers such that N[i] not equal to N[j] for j,i <= N, find an intersect between subarray N[x..y] and N[k..l] for x,y,k,l in N, when elements in N[x..y] are enlarged by a constant factor z
Example:
let say I have an array like this:

 N = [1,3,5,2,6,7,55,14,23,54,56,15,44,11,9,87,10,58,19,17,26, ...]

And let say that I am given an interval I(4,8) and another one II(14,18), that is : 
I(4,8) = [6,7,55,14,23]
II(14,18) = [9,87,10,58,19]

[download]
Now given that the z = 3 the intersect between I and II would be 
I inters II = [9,10,58]

[download]
In the initial array N there cannot be any duplicates and the numbers span from 1..N. I know that I can do this by matching every number in I to every number in II but this would be an algorithm with a nested loop. And that is bad if my arrays are big (as they turn out to be) plus i have to repeat this for a large number of intervals (I'(a,b)) and different z in every iteration.
So my question is: what would be an alternative to this naive approach? Does anyone know how to pre-processes N to make those queries in O(1) time because this would be ideal.

cheers

baxy

In reply to Computing array intersections by baxy77bax

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