[magic_haze]

Both OAG and Innovata provide a dump of all possible flight schedules for the next few months (which includes multiple legs and airlines). It is trivial to add the multiple day/airport feature: I've had a vanilla mysql install (on a P4 with a 1gig ram - my dev machine, sadly) return exactly the sort of stuff you mentioned in less than 100ms, so I'm sure the computational complexity is pretty irrelevant at Google's scale.

[tectonic]

Is any of that data free/cheap for experimentation?

[magic_haze]

A co-founder of the company I did the work for had a few contacts in both companies, so we were able to secure the data through them. It definitely isn't publicly available, but I imagine if you talked to a regional representative at either company, you could get them to generate a sample data dump for you (a gigantic CSV file, for example)

Kayak used to have a free API, but they shut it down "because of constly misuse". I'm not aware of any other service that's targeted at individual developers - most of these APIs are intended for huge companies with correspondingly deep pockets.