first intersection of two arrays of integers - double binary search feasible?
There is a double binary search algorithm.  It will only work is both lists are sorted.  It is basically as follows.


Check the first, lowest number on each list. Compare the numbers to find which number is higher. Assume that higher number is in List A
Take that higher number and do a binary search for it in list B.
If found done.
If not found take the number above the last search location in list B
For example, assume list A had a 5, and in list B you do a binary search and find 6 and 4 with no five in between.  Take the 6 from list B.
Do a binary search for that value is list A.
If found done
If not found take the number above the last search location in list A.
Repeat steps 3&ndash;7 switching back and forth between lists.


That is the basic idea, if you want further information, let me know.