What does “vector<int> Solution::primesum(int n)” mean?

Question

Being a beginner in C++ I am facing a difficulty to understand this thing:

vector<int> Solution::primesum(int n)

Code:

 vector<int> Solution::primesum(int n){
        vector<bool> isprime(n+1);    
  for(int i=0;i<=n;i++)

         isprime[i]=1;
        isprime[0]=0;
        isprime[1]=0;
        for(int i=2;i*i<=n;i++){
            if(isprime[i]){
                for(int j=i*2;j<=n;j+=i)
                 isprime[j]=0;
            }
        }
        vector<int>ans(2);
        for(int i=2;i<=n/2;i++){
            if(isprime[i] && isprime[n-i]){
                ans[0]=i;
                ans[1]=n-i;
                return ans;
            }
        }
    }

Answer 1

Somewhere in your code there must be a class Solution which has a member function primesum taking an integer argument and returning a vector of integer type:

class Solution
{ 
   public:
   vector<int> primesum(int);
};

Only then you can define it outside using scope resolution operator :: :

vector<int> Solution::primesum(int n) 
{ // Definition }

Answer 2

Well, the solution means a class named "Solution" that represents a custom data type. And the primesum(int n) is a member function in the definition of the class with the return type, While the vector is a data type used as an enhanced version of int[] or char[](or string).

class Solution
{
public:
   vector<int> primesum(int) //just like int* primesum(int); amount to returning a array
   ...
};

Solution::vector<int> Solution::primesum(int n){
   ...
}

If possoble, give more details for us to understand and answer your question.