目前的c++还是熟悉数据结构的阶段，所以总结记录下。
作为工具就是，该容器的效率为O(1).常用方法有:
- 赋值 [], =
- empty and size
- begin and end for iterator
- find and count
- insert and modification
#include <unordered_map>
#include <iostream>
#include <vector>
using namespace std;
int main() {
unordered_map<string, vector<int>> keys;
keys["a"] = vector<int>(); // Initialize key with all null vector
keys["a"].push_back(1);
keys["a"].push_back(2);
for (const int &x : keys["a"]){
cout << x << endl;
}
/* Above code is store a int array with string */
/* insert value by [] oper */
unordered_map<string, double> umap;
umap["PI"] = 3.14;
umap["root2"] = 1.414;
umap["user1"] = 2.302;
/* insert value by insert function */
umap.insert(make_pair("e", 2.78));
string key = "PI";
if (umap.find(key) == umap.end())
cout << key << "not found\n\n";
else
cout << "found " << key << "\n";
key = "lambda";
if (umap.find(key) == umap.end())
cout << key << "not found" << "\n";
else
cout << "found " << "\n";
/* iterator elements with iter */
unordered_map<string, double>::iterator iter;
for (iter = umap.begin(); iter !=umap.end(); iter++){
cout << iter->first << " " << iter->second << endl;
}
}