#include <set>

std::set<元素类型> 容器名;

#include <iostream>
#include <set>

int main() {
    // 声明一个整型 set 容器
    std::set<int> mySet;

    // 插入元素
    mySet.insert(10);
    mySet.insert(20);
    mySet.insert(30);
    mySet.insert(40);

    // 输出 set 中的元素
    std::cout << "Set contains: ";
    for (int num : mySet) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    // 查找元素
    if (mySet.find(20) != mySet.end()) {
        std::cout << "20 is in the set." << std::endl;
    } else {
        std::cout << "20 is not in the set." << std::endl;
    }

    // 删除元素
    mySet.erase(20);

    // 再次输出 set 中的元素
    std::cout << "After erasing 20, set contains: ";
    for (int num : mySet) {
        std::cout << num << " ";
    }
    std::cout << std::endl;

    // 检查 set 是否为空
    if (mySet.empty()) {
        std::cout << "The set is empty." << std::endl;
    } else {
        std::cout << "The set is not empty." << std::endl;
    }

    // 输出 set 中元素的数量
    std::cout << "The set contains " << mySet.size() << " elements." << std::endl;

    return 0;
}

Set contains: 10 20 30 40 
20 is in the set.
After erasing 20, set contains: 10 30 40 
The set is not empty.
The set contains 3 elements.