11.3.5

11.27
当我想知道知道，对应关键字的元素有几个的时候，我会使用count
当我只想知道它在不在的时候，我会使用find

11.28

std::map<std::string ,std::vector<int>> hh{ {"p",{0,1,2,3}}   }auto iter= hh.find("p");

11.29
lower_bound和upper_bound 会返回一样的迭代器，指向关键字的插入点
equal_range会返回一个pair，两个迭代器和上面一样

11.30
pos是一个pair
pos.first 是一个迭代器指向关键字匹配的元素
pos.first->second 是元素的第二项，是value部分

11.31
@pezy

#include <map>#include <string>#include <iostream>using std::string;int main(){    std::multimap<string, string> authors{        { "alan", "DMA" },        { "pezy", "LeetCode" },        { "alan", "CLRS" },        { "wang", "FTP" },        { "pezy", "CP5" },        { "wang", "CPP-Concurrency" }    };    // want to delete an element that author is [Alan], work is [112].    string author = "pezy";    string work = "CP5";    auto found = authors.find(author);    auto count = authors.count(author);    while (count) {        if (found->second == work) {            authors.erase(found);            break;           }        ++found;        --count;    }    for (const auto &author : authors)        std::cout << author.first << " " << author.second << std::endl;}

11.32
@pezy

#include <map>#include <set>#include <string>#include <iostream>using std::string;int main(){    std::multimap<string, string> authors{        { "alan", "DMA" },        { "pezy", "LeetCode" },        { "alan", "CLRS" },        { "wang", "FTP" },        { "pezy", "CP5" },        { "wang", "CPP-Concurrency" }    };    std::map<string, std::multiset<string>> order_authors;    for (const auto &author : authors)        order_authors[author.first].insert(author.second);    for (const auto &author : order_authors) {        std::cout << author.first << ": ";        for (const auto &work : author.second)            std::cout << work << " ";        std::cout << std::endl;    }}