Find the intersection point between two sorted arrays with unknown lengths in lesser than O(n)
We need to first find the length of array in long time as it is not given.

Start with length as 1 and increase it as multiple of 2.
Check whether element at length-1 position is positive or not.
If so repeat steps 1 and 2.
If not return the index position it will be the maximum size of the array. As it is mentioned beyond the maximum position element value is negative.
Once the length of array is known simple binary search alto will be applied to search element and it will be searched in both the array and intersection point will be determined.