How make set function faster?

set<unsigned long> k;
unsigned long s = pow(2,31);
for(unsigned long i = 0; i < s; i  ){
    k.insert(i);
}
cout << k.size() << endl;

Code runs very long? So have new method in order to run faster?

CodePudding user response：

How make set function faster?

You can make this faster by using hints, since you know that every insert is to the end of the set:

for(unsigned long i = 0; i < s; i  ){
    k.insert(k.end(), i);
}

Alternatively, you could potentially make it faster using another data structure, such as std::unordered_set for example.

Most significantly, you could make it faster by not creating such a massive set in the first place. For example, if you need to know whether some unsigned long ul is in the set of integers [0, s), then you can simply use ul < s instead of creating the set that contains all the integers.