Спринт 5. Поиск в отсортированном векторе, словаре и множестве. Задание 1.

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

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();
    }
    auto helper = numbers.lower_bound(border);
    if(border>*prev(numbers.end())){
        return prev(numbers.end());
    }
    if (border==*helper || numbers.begin()==helper) {
        return helper;
    }
    if (*helper-border >= border - *prev(helper)) {
        return prev(helper, *helper-border);
    }
    return helper;
}
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;
}