Longest common subsequence: Difference between revisions

{{puzzle}}The '''longest common subsequence''' (or '''LCS''') of groups A and B is the longest group of elements from A and B that are common between the two groups and in the same order in each group. For example, the sequences "1234" and "1224533324" have an LCS of "1234":

For a string example, consider the sequences "thisisatest" and "testing123testing". An LCS would be "tsitest":

 

In this puzzle, your code only needs to deal with strings. Write a function which returns an LCS of two strings (case-sensitive). You don't need to show multiple LCS's.