Question

How to find all intersections (also called the longest common substrings) of two strings and their positions in both strings?

For example, if S1="never" and S2="forever" then resulted intersection must be ["ever"] and its positions are [(1,3)]. If S1="address" and S2="oddness" then resulted intersections are ["dd","ess"] and their positions are [(1,1),(4,4)].

Shortest solution without including any library is preferable. But any correct solution is also welcomed.

Answer 1

Well, you’re saying that you can’t include any library. However, Python’s standard difflib contains a function which does exactly what you expect. Considering that it is a Python interview question, familiarity with difflib might be what the interviewer expected.

In [31]: import difflib

In [32]: difflib.SequenceMatcher(None, "never", "forever").get_matching_blocks()
Out[32]: [Match(a=1, b=3, size=4), Match(a=5, b=7, size=0)]


In [33]: difflib.SequenceMatcher(None, "address", "oddness").get_matching_blocks()
Out[33]: [Match(a=1, b=1, size=2), Match(a=4, b=4, size=3), Match(a=7, b=7, size=0)]

You can always ignore the last Match tuple, since it’s dummy (according to documentation).