C++容器set

定义

std::set - cppreference.cn - C++参考手册

存储唯一的、经过排序的键（key）。set 内部通常基于平衡二叉搜索树（如红黑树）实现，这保证了高效的查找、插入和删除操作

• 唯一性：set 中的每个元素（键）都是唯一的。尝试插入一个已存在的值会失败，容器保持不变
• 有序性：元素在容器中自动排序。默认按升序排列（使用 std::less）
• 键即值：在 set 中，元素本身就是键。它不存储键值对（那是 map 的功能）
• 平衡树实现：通常使用红黑树，保证了 O(log n) 的时间复杂度
• 不可变键：一旦元素插入 set，就不能直接修改其值，因为这会破坏排序。如果需要“修改”，必须先删除再插入新值

构造函数

1、默认构造函数

#include <iostream>
#include <set>
#include <random>using namespace std;int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 10);// 默认构造函数std::set<int> set1;for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

2、带比较函数的构造函数

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 10);// 带比较函数构造函数std::set<int, std::greater<int>> set1;for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

3、区间构造函数

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 100);std::array<int, 2>  arr1 = { 222,333 };// 区间构造函数std::set<int, std::greater<int>> set1(arr1.begin(), arr1.end());for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

4、初始列表构造函数

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 100);// 初始列表构造函数std::set<int, std::greater<int>> set1 = { 1,3,8,1,5,78,5,6 };for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

5、拷贝构造函数

int main()
{system("chcp 65001");std::set<int, std::greater<int>> set2 = { 11,22,33 };// 拷贝构造函数std::set<int, std::greater<int>> set1(set2);cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

6、移动构造函数

int main()
{system("chcp 65001");std::set<int, std::greater<int>> set2 = { 11,22,33 };// 移动构造函数std::set<int, std::greater<int>> set1(std::move(set2));cout << "set2.size()-> " << set2.size() << endl;cout << "set2.empty()-> " << boolalpha << set2.empty() << endl;cout << "set1.size()-> " << set1.size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}
}

迭代器

函数	描述
begin() / end()	返回指向首元素和尾后位置的正向迭代器
rbegin() / rend()	返回指向末元素和首前位置的反向迭代器
cbegin() / cend()	返回常量正向迭代器
crbegin() / crend()	返回常量反向迭代器

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 100);std::set<int, std::greater<int>> set1;for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.max_size()-> " << set1.max_size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;for (auto it : set1){cout << "set1-> " << it << endl;}for (auto it = set1.begin(); it != set1.end(); it++){cout << "begin-end-> " << *it << endl;}for (auto it = set1.cbegin(); it != set1.cend(); it++){cout << "cbegin-cend-> " << *it << endl;}for (auto it = set1.rbegin(); it != set1.rend(); it++){cout << "rbegin-rend-> " << *it << endl;}for (auto it = set1.crbegin(); it != set1.crend(); it++){cout << "crbegin-crend-> " << *it << endl;}
}

查找与计数

函数	描述
find(key)	查找 key，返回指向它的迭代器；未找到返回 s.end()
count(key)	返回 key 在 set 中的数量（0 或 1）
contains(key)	(C++20) 检查 key 是否存在于 set 中，返回 bool
lower_bound(key)	返回指向第一个不小于 key 的元素的迭代器
upper_bound(key)	返回指向第一个大于 key 的元素的迭代器
equal_range(key)	返回一个 std::pair，包含 lower_bound 和 upper_bound 的结果

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 100);std::set<int, std::greater<int>> set1 = { 1,2,3 };for (int i = 1; i < 10; i++){set1.insert(dis(gen));}cout << "set1.size()-> " << set1.size() << endl;cout << "set1.max_size()-> " << set1.max_size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;// 查找auto it = set1.find(2);if (it != set1.end()){cout << "set1.find(2)-> " << *it << endl;}// 计数		cout << "set1.count(2))-> " << set1.count(2) << endl;// 包含cout << "set1.contains(2))-> " << boolalpha << set1.contains(2) << endl;// lower_boundit = set1.lower_bound(2);if (it != set1.end()){cout << "set1.lower_bound(2)-> " << *it << endl;}// upper_boundit = set1.upper_bound(2);if (it != set1.end()){cout << "set1.upper_bound(2)-> " << *it << endl;}// equal_rangeauto pair = set1.equal_range(2);for (auto it = pair.first; it != pair.second; ++it) {std::cout << "equal_range-> " << *it << endl;}
}

修改函数

函数	描述
insert(value)	插入一个元素。返回 std::pair<iterator, bool>，bool 表示是否插入成功
insert(hint, value)	提供插入位置的提示 hint，可能提高效率
emplace(args...)	就地构造一个元素并插入。返回 std::pair<iterator, bool>
erase(key)	删除值为 key 的元素，返回删除的元素数量（0 或 1）
erase(it)	删除迭代器 it 指向的元素
erase(first, last)	删除范围 [first, last) 的元素
clear()	删除所有元素
swap(other)	与另一个 set 交换内容

int main()
{system("chcp 65001");std::random_device rd;std::mt19937 gen(rd());std::uniform_int_distribution<> dis(1, 100);std::set<int, std::greater<int>> set1 = { 1,2,3 };for (int i = 1; i < 10; i++){set1.insert(dis(gen));}set1.emplace(123);cout << "set1.size()-> " << set1.size() << endl;cout << "set1.max_size()-> " << set1.max_size() << endl;cout << "set1.empty()-> " << boolalpha << set1.empty() << endl;// 删除set1.erase(1);set1.erase(set1.begin());set1.erase(set1.begin(), --set1.end());for (auto it : set1){cout << "set1-> " << it << endl;}set1.clear();
}

其他

操作	时间复杂度
insert / emplace	O(log n)
erase (键)	O(log n)
erase (迭代器)	O(1) 摊销 (删除单个元素)
find / count	O(log n)
lower_bound / upper_bound	O(log n)
size / empty	O(1)
begin / end	O(1)