18.查询效率最高的unordered_map

 #include <string>
 #include <iostream>
 //查询性能最高
 //增删查改与map是一样的,但是本质区别就是unordered_map底层是hash表,map底层是红黑树
 #include <unordered_map>
 using namespace std;

 void main()
 {
     unordered_map<string, double>mymap{ {"a1",},{ "a2", },{ "a3", } };

     //不允许重复
     mymap.insert(pair<string, double>("a4", ));

     mymap.insert(unordered_map<string, double>::value_type("a5", ));

     for (auto i : mymap)
     {
         cout << i.first << "  " << i.second << endl;
     }

     auto it = mymap.find("a1");
     if (it != mymap.end())
     {
         cout << it->second << endl;
     }
     cin.get();
 }