unordered_set

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> s;
    auto a = s.insert(5);
    auto b = s.insert(5);
    std::cout << std::boolalpha << a.second << ' ' << b.second << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<std::string> blocked{"spam", "junk"};
    std::cout << blocked.count("spam") << '\n';
    std::cout << blocked.count("ok") << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> s{1, 2, 3};
    s.erase(2);
    std::cout << "count 2: " << s.count(2) << '\n';
    std::cout << "size: " << s.size() << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    int data[] = {3, 7, 1, 7, 9};
    std::unordered_set<int> seen;
    for (int x : data) {
        if (!seen.insert(x).second) {
            std::cout << "first duplicate: " << x << '\n';
            break;
        }
    }
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> s{10, 20, 30};
    int total = 0;
    for (int x : s) total += x;
    std::cout << "sum = " << total << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>
#include <vector>

int main() {
    std::vector<int> v{1, 2, 2, 3, 3, 3};
    std::unordered_set<int> u(v.begin(), v.end());
    std::cout << u.size() << " unique\n";
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<std::string> s{"alpha", "beta"};
    auto it = s.find("beta");
    std::cout << (it != s.end() ? *it : "none") << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> s{1, 2, 3};
    s.clear();
    std::cout << std::boolalpha << s.empty() << '\n';
    return 0;
}

#include <iostream>
#include <unordered_set>

int main() {
    std::unordered_set<int> a{1, 2, 3, 4};
    std::unordered_set<int> b{3, 4, 5};
    for (int x : a) if (b.count(x)) std::cout << x << ' ';
    std::cout << '\n';
    return 0;
}