Given a time (eg. currently 4:24pm on Tuesday), I’d like to be able to select all businesses that are currently open out of a set of businesses.
- I have the open and close times for every business for every day of the week
- Let’s assume a business can open/close only on 00, 15, 30, 45 minute marks of each hour
- I’m assuming the same schedule each week.
- I am most interested in being able to quickly look up a set of businesses that is open at a certain time, not the space requirements of the data.
- Mind you, some my open at 11pm one day and close 1am the next day.
- Holidays don’t matter – I will handle these separately
What’s the most efficient way to store these open/close times such that with a single time/day-of-week tuple I can speedily figure out which businesses are open?
I am using Python, SOLR and mysql. I’d like to be able to do the querying in SOLR. But frankly, I’m open to any suggestions and alternatives.
If you are willing to just look at single week at a time, you can canonicalize all opening/closing times to be set numbers of minutes since the start of the week, say Sunday 0 hrs. For each store, you create a number of tuples of the form [startTime, endTime, storeId]. (For hours that spanned Sunday midnight, you’d have to create two tuples, one going to the end of the week, one starting at the beginning of the week). This set of tuples would be indexed (say, with a tree you would pre-process) on both startTime and endTime. The tuples shouldn’t be that large: there are only ~10k minutes in a week, which can fit in 2 bytes. This structure would be graceful inside a MySQL table with appropriate indexes, and would be very resilient to constant insertions & deletions of records as information changed. Your query would simply be ‘select storeId where startTime <= time and endtime >= time’, where time was the canonicalized minutes since midnight on sunday.
If information doesn’t change very often, and you want to have lookups be very fast, you could solve every possible query up front and cache the results. For instance, there are only 672 quarter-hour periods in a week. With a list of businesses, each of which had a list of opening & closing times like Brandon Rhodes’s solution, you could simply, iterate through every 15-minute period in a week, figure out who’s open, then store the answer in a lookup table or in-memory list.