JuniorTheoryCommon

What does the program print?

C++

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v{2, 3, 1, 3};
    std::sort(v.begin(), v.end(), [](int a, int b) { return a > b; });
    for (int x : v) {
        std::cout << x << ' ';
    }
}

3 3 2 1

Expecting 1 2 3 3: the comparator returns true when a must stand before b, so a > b puts the larger numbers first.
Expecting 3 2 1: std::sort only reorders the elements and keeps both 3s; duplicates disappear in a std::set, not in a sort.

Why must this comparator use > and not >=?
How would you sort v in descending order without writing a lambda?

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JuniorTheoryCommon

What does the program print?

C++

#include <algorithm>
#include <iostream>
#include <vector>

int main() {
    std::vector<int> v{2, 3, 1, 3};
    std::sort(v.begin(), v.end(), [](int a, int b) { return a > b; });
    for (int x : v) {
        std::cout << x << ' ';
    }
}

3 3 2 1

Expecting 1 2 3 3: the comparator returns true when a must stand before b, so a > b puts the larger numbers first.
Expecting 3 2 1: std::sort only reorders the elements and keeps both 3s; duplicates disappear in a std::set, not in a sort.

Why must this comparator use > and not >=?
How would you sort v in descending order without writing a lambda?

Back to questions Open topic in roadmap →Answer it yourself — Quiz