C++: What is faster - lookup in hashmap or switch statement?

Question

I have a code pattern which translates one integer to another. Just like this:

int t(int value) {
    switch (value) {
        case 1: return const_1;
        ca         


        

Answer 1

Hash table time complexity is generally O(1) when don't considering collision. C++ standard doesn't specified how switch is implemented but it can be implemented as jump-table which time complexity is O(1) too or it can be implemented as binary search which time complexity is O(log n) or a combination depending on how many case statement etc.

So in a word, small scale like your case, switch is faster, but hash table might win in large scale