1449 — Dominating Patterns

String Matching
String Multimatching

Take a look at this page: http://www.ahmed-aly.com/Category.jsp?ID=35. The first and fourth problems are a bit simpler than what you described (you just have to answer whether B_i appears in A). The second is similar to them but takes place in a grid. The third is also slightly easier than what you described. I guess you're probably interested in them, though, because the idea is the same — just a small modification.

Anyway, Frequency Count is pretty much equivalent to what you're asking. Finally, I'd like to recommend USACO — Censoring (Gold Division), which is about the same difficulty. It's nice because it forces you to notice something important to avoid receiving TLE in a given testcase.