I just skimmed through those posts. Indeed interesting, but I couldn't find what type of data-structure they use for their main search (as opposed to instant search suggestions).
For each document, we extract the list of words and build a hash-table that associates words to documents
When all documents are processed, we compute an on-disk binary data-structure containing the mapping of words to documents. This data-structure is the index we will use to process queries.
Part 1: https://blog.algolia.com/inside-the-algolia-engine-part-1-in...
No affiliation, just thought they were really interesting.