The intersection of two lists L1 and L2, L1 ∩ L2, is defined as
the list containing elements in both L1 and L2 only. Given
two sorted lists L1 and L2, write a function, called intersection,
to compute L1 ∩ L2 using only the basic list operations.
The intersection function is defined as follows template list
intersection( const list & L1, const list & L2);
C++