C++中unordered_multiset容器用法示例详解

#include <unordered_set>
using namespace std;

unordered_multiset<int> ums1;                  // 空unordered_multiset
unordered_multiset<string> ums2 = {"a", "b", "a"}; // 初始化列表(允许重复)
unordered_multiset<double> ums3(10);           // 初始桶数为10

unordered_multiset<int> numbers;

int arr[] = {1, 2, 2, 3, 3, 3};
unordered_multiset<int> nums(arr, arr+6);

unordered_multiset<int> ums2(ums1);

struct CaseInsensitiveHash {
    size_t operator()(const string& s) const {
        size_t h = 0;
        for(char c : s) {
            h += tolower(c);
        }
        return h;
    }
};

struct CaseInsensitiveEqual {
    bool operator()(const string& a, const string& b) const {
        if(a.length() != b.length()) return false;
        for(size_t i = 0; i < a.length(); ++i) {
            if(tolower(a[i]) != tolower(b[i])) return false;
        }
        return true;
    }
};

unordered_multiset<string, CaseInsensitiveHash, CaseInsensitiveEqual> case_insensitive_ms;

cout << ums.size();  // 返回元素总数量(包括重复)

if(ums.empty()) {
    cout << "unordered_multiset is empty";
}

cout << ums.max_size();  // 返回可容纳的最大元素数

for(auto it = ums.begin(); it != ums.end(); ++it) {
    cout << *it << " ";
}

ums.insert(10);                   // 插入单个元素
ums.insert({5, 5, 15});           // 插入初始化列表(允许重复)
ums.insert(arr, arr+3);           // 插入范围
auto it = ums.insert(20);         // 返回指向插入元素的迭代器

auto it = ums.emplace(30);        // 原地构造元素

ums.erase(5);                     // 删除所有值为5的元素
auto it = ums.find(10);
if(it != ums.end()) {
    ums.erase(it);                // 只删除一个10
}
ums.erase(ums.begin(), ums.end()); // 删除范围

ums.clear();  // 清空所有元素

unordered_multiset<int> ums2;
ums.swap(ums2);  // 交换两个unordered_multiset

auto it = ums.find(10);  // 返回指向第一个10的迭代器
if(it != ums.end()) {
    cout << "Found: " << *it;
}

cout << ums.count(5);  // 返回元素5的数量

auto range = ums.equal_range(15);  // 返回等于15的元素范围[pair]
for(auto it = range.first; it != range.second; ++it) {
    cout << *it << " ";
}

cout << ums.bucket_count();  // 返回桶的数量

cout << ums.max_bucket_count();  // 返回最大桶数

cout << ums.bucket_size(2);  // 返回第2个桶中的元素数

cout << ums.bucket("apple");  // 返回"apple"所在的桶索引

cout << ums.load_factor();  // 返回负载因子(元素数/桶数)

cout << ums.max_load_factor();  // 返回最大负载因子
ums.max_load_factor(0.75);      // 设置最大负载因子

ums.rehash(20);  // 设置桶数为至少20

ums.reserve(100);  // 预留空间至少容纳100个元素

#include <iostream>
#include <unordered_set>
#include <string>
using namespace std;

int main() {
    // 创建并初始化unordered_multiset
    unordered_multiset<string> words = {"apple", "banana", "apple", "orange", "banana"};
    
    // 插入元素
    words.insert("grape");
    words.emplace("pear");
    words.insert({"apple", "kiwi", "kiwi"});
    
    // 查找元素
    cout << "Number of 'apple': " << words.count("apple") << endl;
    
    auto found = words.find("orange");
    if(found != words.end()) {
        cout << "Found orange at bucket #" << words.bucket(*found) << endl;
    }
    
    // 遍历unordered_multiset
    cout << "All words: ";
    for(const auto& word : words) {
        cout << word << " ";
    }
    cout << endl;
    
    // 使用equal_range处理重复元素
    cout << "All apples: ";
    auto range = words.equal_range("apple");
    for(auto it = range.first; it != range.second; ++it) {
        cout << *it << " ";
    }
    cout << endl;
    
    // 删除元素
    words.erase("banana");  // 删除所有banana
    auto it = words.find("kiwi");
    if(it != words.end()) {
        words.erase(it);    // 只删除一个kiwi
    }
    
    // 桶信息
    cout << "\nBucket information:" << endl;
    cout << "Number of buckets: " << words.bucket_count() << endl;
    cout << "Current load factor: " << words.load_factor() << endl;
    
    // 调整哈希表
    words.rehash(15);
    cout << "After rehash, bucket count: " << words.bucket_count() << endl;
    
    // 容量信息
    cout << "\nSize: " << words.size() << endl;
    cout << "Is empty: " << (words.empty() ? "Yes" : "No") << endl;
    
    return 0;
}