Handle multi-source string matching and tagging

Question

Given an LLM output string and a list of source strings, design an algorithm to count how many times each source appears in the output. Extend the solution to return the output string where every occurrence of a source string is wrapped in <tag></tag> while correctly handling overlapping matches. Modify the algorithm so that each tag also includes annotations of the indices of the sources that matched (e.g., <tag>text</tag>[1][3]).