Fastest possible string key lookup for known set of keys

Question

Consider a lookup function with the following signature, which needs to return an integer for a given string key:

int GetValue(string key) { ... }
         


        

Answer 1

Consider using Knuth–Morris–Pratt algorithm.

Pre-process given map to a large string like below

String string = "{foo:1}{bar:42}{bazz:314159}";
int length = string.length();

According KMP preprocessing time for the string will take O(length). For searching with any word/key will take O(w) complexity, where w is length of the word/key.

You will be needed to make 2 modification to KMP algorithm:

• key should be appear ordered in the joined string
• instead of returning true/false it should parse the number and return it

Wish it can give a good hints.