map容器

map容器封装了红黑树，用于查找。
头文件

#include<map>

map容器初始化

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

int main() {
    // 1. 创建一个空的map容器
    map<int,string> m1;

    // 2. 使用统一初始化列表
    map<int,string> m2({{1, "aa"}, {2, "bb"}, {3, "cc"},{4, "dd"},{5, "ee"}});
    for(auto& val:m2) {
        cout<<"key = "<<val.first<<"  value = "<<val.second<<endl;
    }

    // 3. 拷贝构造函数初始化
    map<int,string> m3 = m2;
    for(auto& val:m3) {
        cout<<"key = "<<val.first<<"  value = "<<val.second<<endl;
    }

    // 4. 用迭代器初始化
    auto begin = m3.begin(); begin++;
    auto end = m3.end(); end--;
    map<int,string> m4(begin, end);
    return 0;
}

map容器特性操作

• size 大小
• empty 是否为空
• clear 清空容器

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

int main() {
    map<int,string> m1({{1, "aa"}, {2, "bb"}, {3, "cc"},{4, "dd"},{5, "ee"}});
    cout << "m1.size = "<<m1.size() <<endl;
    cout << "m1.empty = "<<m1.empty() <<endl;
    m1.clear();
    cout << "m1.size = "<<m1.size() <<endl;
    return 0;
}

map查找元素

在容器中寻找值为k的元素，返回该元素的迭代器。否则，返回map.end()。

iterator find (const key_type& k);
const_iterator find (const key_type& k) const;

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

int main() {
    map<int,string> m1({{1, "aa"}, {2, "bb"}, {3, "cc"},{4, "dd"},{5, "ee"}});
    m1.erase(1); // 从m1容器中删除指定key的元素，返回已删除元素的个数
    // map<int,string>::iterator it = m1.find(99);
    map<int,string>::iterator it = m1.find(2);
    if (it != m1.end())
    {
        cout <<"value = "<<it->second<<endl;
        m1.erase(it); // 删除该元素， 返回下一个有效的迭代器
    } else {
        cout <<"no element was founded "<< endl;
    }
  
    return 0;
}

map容器插入

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

int main() {
    map<int,string> m1;
    // 1. 用初始化列表在容器中插入多个元素
    m1.insert({{1, "aa"}, {2, "bb"}});
    m1.insert({make_pair<int,string>(3, "ccc"), pair<int,string>(4, "ddd")});
   

    // 2. 插入一个元素,返回一个pair，first是已插入元素的迭代器，second是插入结果bool类型
    auto ret = m1.insert({1, "eeeeeeee"});
    if (ret.second == true)
    {
        cout <<"插入成功ret.first = "<<ret.first->first<<"  ret.second = "<<ret.first->second<<endl;
    } else {
        cout <<"插入失败"<<endl;
    }

    // 3. 用迭代器插入一个区间的元素
    map<int,string> m2({{11, "111"}, {12, "121212"}, {13, "131313"},{14, "141414"},{15, "151515"}});
    m1.insert(m2.begin()++,m2.end()--);

    // 4. 使用emplace 效率更高
    auto ret1 = m1.emplace(pair<int,string>(20, "eeeeeeee"));
    if (ret1.second == true)
    {
        cout <<"插入成功ret1.first = "<<ret1.first->first<<"  ret1.second = "<<ret1.first->second<<endl;
    } else {
        cout <<"插入失败"<<endl;
    }

    for(auto& val:m1) {
        cout<<"key = "<<val.first<<"  value = "<<val.second<<endl;
    }
    return 0;
}