How to correct the user input (Kind of google “did you mean?”)

Question

I have the following requirement: -

I have many (say 1 million) values (names). The user will type a search string.

I don\'t expect the user to spell the names c

Answer 1

the Bitap Algorithm is designed to find an approximate match in a body of text. Maybe you could use that to calculate probable matches. (it's based on the Levenshtein Distance)

(Update: after having read Ben S answer (use an existing solution, possibly aspell) is the way to go)

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As others said, Google does auto correction by watching users correct themselves. If I search for "someting" (sic) and then immediately for "something" it is very likely that the first query was incorrect. A possible heuristic to detect this would be:

• If a user has done two searches in a short time window, and
• the first query did not yield any results (or the user did not click on anything)
• the second query did yield useful results
• the two queries are similar (have a small Levenshtein distance)

then the second query is a possible refinement of the first query which you can store and present to other users.

Note that you probably need a lot of queries to gather enough data for these suggestions to be useful.

Answer 2

I would consider using a pre-existing solution for this.

Aspell with a custom dictionary of the names might be well suited for this. Generating the dictionary file will pre-compute all the information required to quickly give suggestions.