Re: Fast NSArray compare
Re: Fast NSArray compare
- Subject: Re: Fast NSArray compare
- From: Graham Cox <email@hidden>
- Date: Tue, 15 Apr 2014 10:59:42 +1000
On 15 Apr 2014, at 10:02 am, Varun Chandramohan <email@hidden> wrote:
> Lets say I walkthrough 1000 files and folders, for each file/folder I need to compare against this array list. This might be slow or inefficient. Is there a faster way to do something like this?
As a general principle, if you have to check whether one of a list of things is part of another list of things, an array is the wrong container for the job, because it amounts to a worst-case O(n^2) search. Instead, use a set or hash table for the set of things that must be detected among the first list, and it reduces to a worst-case O(n) operation. That said, if the number of items in the second list is small, the performance may be acceptable, and using a hash table might not speed it up noticeably - the time will be dominated by the iteration through the larger list.
--Graham
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