поиск сортированый пизжено

#include <iostream>
#include <string>
#include <algorithm>
#include <set>

using namespace std;

set<int>::const_iterator FindNearestElement(const set<int>& numbers, int border) {
    // set<int>::const_iterator — тип итераторов для константного множества целых чисел
    if (numbers.empty()){return numbers.end();}
    if (border <= *numbers.begin()){return numbers.begin();}
    if (border >= *prev(numbers.end(), 1)){return prev(numbers.end());}
    auto it = numbers.lower_bound(border);
    if (border == *it){return it;}
    if (border - *prev(it, 1) <= *it - border){
        return prev(it, 1);
    }
    return it;
}

int main() {
    set<int> numbers = {1, 4, 6};
    cout << *FindNearestElement(numbers, 0) << " " << *FindNearestElement(numbers, 3) << " "
         << *FindNearestElement(numbers, 5) << " " << *FindNearestElement(numbers, 6) << " "
         << *FindNearestElement(numbers, 100) << endl;
    set<int> empty_set;
    cout << (FindNearestElement(empty_set, 8) == end(empty_set)) << endl;
    return 0;
}