Magdoll wrote: > Hi, > > I have to read through a file that will give me a bunch of intervals. > My ultimate goal is to produce a final set of intervals such that not > two intervals overlap by more than N, where N is a predetermined > length. > > For example, I could read through this input: > (1,10), (3,15), (20,30),(29,40),(51,65),(62,100),(50,66) > > btw, the input is not guaranteed to be in any sorted order. > > say N = 5, so the final set should be > (1,15), (20, 30), (29, 40), (50, 100) > Hi,
The problem, as stated here, may have several solutions. For instance the following set of intervals also satisfies the constraint: (1,15), (20,40), (50,100) One question you should ask yourself is: do you want all solutions? or just one? If you want just one, there's another question: which one? the one with the most intervals? any one? If you want all of them, then I suggest using prolog rather than python (I hope I won't be flamed for advocating another language here). > Is there already some existing code in Python that I can easily take > advantage of to produce this? Right now I've written my own simple > solution, which is just to maintain a list of the intervals. I can use > the Interval module, but it doesn't really affect much. I read one > interval from the input file at a time, and use bisect to insert it in > order. The problem comes with merging, which sometimes can be > cascading. > > ex: > read (51,65) ==> put (51,65) in list > read (62,100) ==> put (62,100) in list (overlap only be 4 <= N) > read (50,66) ==> merge with (51,65) to become (50,66) ==> now can > merge with (62,100) The way this algorithm is presented suggests an additional constraint: you cannot merge two intervals if their overlap <= N. In that case, there is a single solution indeed... Nitpick: you cannot merge (50,66) and (62,100) since their overlap is still <= 5. If you have a reasonable number of intervals, you're algorithm seems fine. But it is O(n**2), so in the case you read a lot of intervals and you observe unsatisfying performances, you will have to store the intervals in a cleverer data structure, see one of these: http://en.wikipedia.org/wiki/Interval_tree http://en.wikipedia.org/wiki/Segment_tree Cheers, RB -- http://mail.python.org/mailman/listinfo/python-list
