Fast and elegant one-way mapping of known integer values

c++

Solution

Use a map

#include <map>
#include <iostream>

int main() {
   std::map <int, int> m;
   m[79] = 12958; 
   std::cout << m[79] << std::endl;
}

Using a map is the most general solution and the most portable (the C++ standard does not yet support hash tables, but they are a very common extension). It isn't necessariily the fastest though. Both the binary search and the hashmap solutions suggested by others may (but not will) out-perform it. This probably won't matter for most applications, however.

Problem

I have to map a set of known integers to another set of known integers, 1-to-1 relationship, all predefined and so on. So, suppose I have something like this (c++, simplified, but you'll get the idea): ``` struct s { int a; int b; }; s theMap[] = { {2, 5}, {79, 12958 } }; ``` Now given an input integer, say 79, I'd need to find the corresponding result from theMap (obviously 12958). Any nice and fast method of doing this, instead of your run-of-the-mill for loop? Other data structure suggestions are also welcome, but the map should be easy to write in the source by hand. The values in both sets are in the range of 0 to 2^16, and there are only about 130 pairs. What I also am after is a very simple way of statically initializing the data.

Original source