public class RigidityFncSubsequence
extends RigidityFnc
Implementation for rigidity function with subsequence matching.
Let m be the number of left term atoms and n be the number of right term
atoms.
Time complexity = Exponential worst case (back tracking) but should be OK in
average case
Space complexity = O(m * n)
This implementation reuses all the allocated objects for performance reasons.
That's why the space complexity will become the quadratic maximum of all m's
and n's. O(max(m1, ..., mk) * max(n1, ..., nk))
