Shared Playlist History

medium

Two friends compare their listening histories. Each history is a string where every character is a track code, in the order it was played. A shared run is a sequence of track codes that appears in both histories in the same relative order — gaps are fine, reordering is not.

Given histories a and b, return the length of the longest shared run.

Example 1

in a = "abcde", b = "ace"

out 3

Both played "a", then "c", then "e" in that order.

Example 2

in a = "abc", b = "def"

out 0

No track code appears in both.

Constraints

· 0 <= len(a), len(b) <= 50
· lowercase track codes only