두 개 뽑아서 더하기

#include <string>
#include <vector>
#include <algorithm>

using namespace std;

vector<int> solution(vector<int> numbers) 
{
    vector<int> answer;
    int i, j, size = numbers.size();
    
    for(i = 0; i < size; i++)
    {
        for(j = i+1; j < size; j++)
        {
            answer.push_back(numbers[i] + numbers[j]);
        }
    }
    sort(answer.begin(), answer.end());
    auto it = unique(answer.begin(), answer.end());
    answer.erase(it, answer.end());
    
    return answer;
}