搜索字符串的最快方法

Question

I have 300 strings to be stored and searched for and that most of them are identical in terms of characters and lenght. For Example i have string "ABC1","ABC2","ABC3" and so on. and another set like sample1,sample2,sample3. So i am kinda confused as of how to store them like to use an array or a hash table. My main concern is the time i take to search for a string when i need to get one out from the storage. If i use an array i will have to do a string compare on all the index for me to arrive at one. Now if i go and impliment a hash table i will have to take care of collisions(obvious) and that i will have to impliment chaining for storing identical strings.

So i am kind of looking for some suggestions weighing the pros and cons of each and arrive at the best practice

Answer 1

Because the keys are short tend to have a common prefix you should consider radix data structures such as the Patricia trie and Ternary Search Tree (google these, you'll find lots of examples) Time for searching these structures tends to be O(1) with respect to # of entries and O(n) with respect to length of the keys. Beware, however that long strings can use lots of memory.

Search time is similar to hash maps if you don't consider collision resolution which is not a problem in a radix search. Note that I am considering the time to compute the hash as part of the cost of a hash map. People tend to forget it.

One downside is radix structures are not cache-friendly if your keys tend to show up in random order. As someone mentioned, if the search time is really important: measure the performance of some alternative approaches.

Answer 2

This depends on how much your data is changing. With that I mean, if you have 300 index strings which are referencing to another string, how often does those 300 index strings change?

You can use a std::map for quick lookups, but the map will require more resource when it is created the first time (compared to a array, vector or list).

I use maps mostly for some kind of dynamic lookup tables (for example: ip to socket).

So in your case it will look like this:

std::map<std::string, std::string> my_map;
my_map["ABC1"] = "sample1";
my_map["ABC2"] = "sample2";

std::string looked_up = my_map["ABC1"];