巧用nth_element求容器前n%大小的那个数

#include <algorithm>
#include <vector>
#include <iostream>
#include <string>
#include <numeric>
std::string::size_type stringLengthSum(std::string::size_type sumSoFar, const std::string& s)
{
    return sumSoFar += s.size();
}
int main()
{
    std::vector<int> v{1,2,3,4,5,6,7,8,9,10,11,12};
    auto begin = v.begin();
    auto end = v.end();
    decltype(begin) goodPosition;
    goodPosition = begin + 0.3 * v.size();
    nth_element(begin, goodPosition, end);
    std::cout << *goodPosition << std::endl;
    return 0;
}