map & unordered_map

map

#include <bits/stdc++.h> //map的基本操作如下
using namespace std;

int main()
{
    // 构造函数
    map <string,int> dict;
    //   下标类型 存储的值的类型  

    // 插入数据的三种方式
    dict.insert(pair <string,int> ("apple",2));
    dict.insert(map <string, int> :: value_type("orange",3));
    dict["banana"] = 6;

    // 判断是否有元素
    if(dict.empty())
        cout<<"该字典无元素"<<endl;
    else
        cout<<"该字典共有"<<dict.size()<<"个元素"<<endl;

    // 遍历
    map <string,int> :: iterator iter;
    for(iter = dict.begin();iter != dict.end();iter++)
    {
        cout << iter->first << ends << iter->second << endl;
    }

    // 查找
    if((iter = dict.find("banana")) != dict.end()) //  返回一个迭代器指向键值为key的元素，如果没找到就返回end()
        cout << "已找到banana,其value为" << iter->second << "." << endl;
    else
        cout << "未找到banana." << endl;

    if(dict.count("watermelon") == 0) // 返回键值等于key的元素的个数
        cout << "watermelon不存在" << endl;
    else
        cout << "watermelon存在" << endl;

    pair <map<string,int> :: iterator, map<string,int> :: iterator> ret;
    ret = dict.equal_range("banana"); // 查找键值等于 key 的元素区间为[start,end)，指示范围的两个迭代器以 pair 返回
    cout << ret.first->first << ends << ret.first->second << endl;
    cout << ret.second->first << ends << ret.second->second << endl;

    iter = dict.lower_bound("boluo"); // 返回一个迭代器，指向键值>=key的第一个元素。
    cout << iter->first << endl;
    iter = dict.upper_bound("boluo"); // 返回一个迭代器，指向值键值>key的第一个元素。
    cout << iter->first << endl;
    return 0;
}

unordered_map

#include<bits/stdc++.h>    
using namespace std;  

int main()
{
    unordered_map <string,int> dict; // 声明unordered_map对象

    // 插入数据的三种方式
    dict.insert(pair<string,int>("apple",2));
    dict.insert(unordered_map<string, int>::value_type("orange",3));
    dict["banana"] = 6;

    // 判断是否有元素
    if(dict.empty())
        cout<<"该字典无元素"<<endl;
    else
        cout<<"该字典共有"<<dict.size()<<"个元素"<<endl;

    // 遍历
    unordered_map <string,int> :: iterator iter;
    for(iter = dict.begin();iter != dict.end();iter++)
        cout << iter->first << ends << iter->second << endl;

    // 查找
    if(dict.count("boluo") == 0)
        cout << "can't find boluo!" << endl;
    else
        cout << "find boluo!" << endl;

    if((iter = dict.find("banana")) != dict.end())
        cout << "banana=" << iter->second << endl;
    else
        cout << "can't find boluo!" << endl;

    return 0;
}

CSDN讲解

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