【C++STL】map / multimap 保姆级教程：从底层原理到实战应用!

#include<iostream>
#include<map>
using namespace std;
void test_map1()
{
	//无参默认构造
	map<string, string> dict;
	//初始化列表构造
	map<string, string> dict1 = { {"left","左边"},{"right","右边"},{"sort","排序"} };
	//拷贝构造
	map<string, string> dict2(dict1);
	//迭代器区间构造
	map<string, string> dict3(dict1.begin(), dict1.end());
}

#include<iostream>
#include<map>
using namespace std;
void test_map2()
{
	
	//初始化列表构造
	map<string, string> dict1 = { {"left","左边"},{"right","右边"},{"sort","排序"} };
	//正向遍历
	for (auto& e : dict1)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;

	//反向迭代
	auto it = dict1.rbegin();
	while (it != dict1.rend())
	{
		//map中的key是不能被修改的 只有value能被修改
		//(*it).first = "xxx";//key不能被修改！！！
		//(*it).second = "xxxx";
		cout << (*it).first << ":" << (*it).second << " ";
		//cout << it->first << ":" << it->second<< " ";

		it++;
	}
	cout << endl;


	for (auto&[k, v] : dict)
	{
		cout << k<< ":" << v<< endl;
	}

	// 结构化绑定 C++14/17
	auto [x, y] = kv1;
	auto& [x1, y1] = kv1;
	x1 += 'x';
	x += 'k';
}

#include<iostream>
#include<map>
using namespace std;
void test_map3()
{
	//map底层其实存的是pair(键值对)
	pair<string, string> kv1("left", "左边");
	pair<string, string> kv2("right", "右边");
	pair<string, string> kv3("sort", "排序");
	pair<string, string> kv4("const", "常量");
	map<string, string> dict = { kv1,kv2,kv3,kv4 };

	dict.insert({"left","哈哈"});//若键'left'已经存在则插入失败
	dict.insert(pair<string, string>("sort", "排序"));//插入一个pair
		dict.insert(make_pair("hello", "你好"));//插入还可以使用make_pair
	dict.insert({ "people","人" });//隐式类型转化

	//列表插入
	auto pos=dict.begin();
	dict.insert(pos,{"English","英文"});

	vector<pair<string,string>> v={{"k1","v1"},{"k2","v2"},{"k3","v3"}};

	//迭代器区间插入
	dict.insert(v.begin(),v.end());

	for(const auto& e:dict )
	{
		cout<<e.first<<":"<<e.second<<" ";
	}
	cout<<endl;
}

void test_map4()
{
	string arr[] = {"苹果" ,"香蕉","梨","草莓","香蕉","梨" ,"苹果","梨","苹果"};
	map<string, int> m;

	for (auto& str : arr)
	{
		//map<string, int>::iterator it = m.find(str);
		auto it = m.find(str);
		if (it != m.end())
		{
			//找到了 就加加
			it->second++;
		}
		else
		{
			//没找到就插入
			m.insert({str,1});
		}

	}
	for (auto& e : m)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;

	string arr2[] = { "苹果" ,"香蕉","梨","草莓","香蕉","梨" ,"苹果","梨","苹果" };
	map<string, int> m2;
	//使用count也可以代替find
	for (auto& e : arr)
	{
		
		if (m2.count(e))
		{
			//如果元素已经存在 ++该key对应的value值即可
			m2[e]++;//operator[]的使用会在后面介绍
		}
		else
		{
			//没找到就插入
			m2.insert({ e,1 });
		}
	}

	for (auto& e : m2)
	{
		cout << e.first <<":" << e.second << " ";
	}
	cout << endl;
	
	//删除一个指定的key
	m.erase("草莓");
	for (auto& e : m)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;

	//删除一个迭代器位置的key 注意key被删除了那么value也跟着直接被删除了！！！
	auto pos = m.find("香蕉");
	if (pos != m.end())
	{
		m.erase(pos);
	}
	for (auto& e : m)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;

	//删除一段迭代器区间的key
	m2.erase(m2.begin(), m2.end());
}

#include<iostream>
#include<map>
using namespace std;
void test_map5()
{
	map<int, string> m = { {1,"a"},{2,"b"},{3,"c"},{5,"e"},{4,"d"},{6,"f"}};
	auto pos1 = m.lower_bound(2);
	auto pos2 = m.upper_bound(4);

	while (pos1 != pos2)
	{
		cout << pos1->first << ":" << pos1->second << " ";
		pos1++;
	}
	cout << endl;


	auto pos3 = m.lower_bound(2);
	//可以删除这段区间的值 注意不能再用上面的pos1了因为pos已经改变了
	m.erase(pos3, pos2);
	for (auto& e : m)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;
}

#include<iostream>
#include<map>
using namespace std;
void test_map6()
{
	map<string, string> dict = { {"left", "左边"}, {"right", "右边"}, {"insert", "插入"},{ "string", "字符串" } };

	//=======================================================================
	// 1、如果k不在map中，insert会插⼊k和mapped_type默认值，同时[]返回结点中存储
	//mapped_type值的引⽤，那么我们可以通过引⽤修改返映射值。所以[]具备了插⼊+修改功能
	//2、如果k在map中，insert会插⼊失败，但是insert返回pair对象的first是指向key结点的
	//迭代器，返回值同时[]返回结点中存储mapped_type值的引⽤，所以[]具备了查找+修改的功能
	//=======================================================================
	dict["set"]; // 插入一个空字符，string的无参构造不传参构造出一个空字符串
	dict["set"] = "集合"; // 修改
	dict["string"] = "xxxx"; // 修改
	dict["begin"] = "开始"; // 插入+修改
	//cout << dict["set"] << endl; // 查找
	

	string arr[] = { "苹果", "西瓜", "苹果", "西瓜", "苹果", "苹果", "西瓜","苹果", "香蕉", "苹果", "香蕉" };
	map<string, int> countMap;
	for (auto& str : arr)
	{
		//直接使用operator[] 如果key在那么就对key的value++ 如果key不在那就直接插入
		countMap[str]++;
	}

	//结构化绑定
	for (auto& [k, v] : countMap)
	{
		cout << k << ":" << v << endl;
	}
}

#include<iostream>
#include<map>
using namespace std;
void test_multimap()
{

	multimap<string, string> dict = { {"left", "左边"}, {"right", "右边"}, {"insert", "插入"},{ "string", "字符串" } };
	//插入相同的key
	dict.insert({"apple", "苹果"});
	dict.insert({ "apple", "haha" });
	dict.insert({ "apple", "hehe" });
	dict.insert({ "string", "xxxx" });


	dict.erase("apple");//删除指定的key相应的value也会被直接删除
	auto pos = dict.find("string");
	if(pos != dict.end())
	{
		dict.erase(pos);
	}



	for (auto& e : dict)
	{
		cout << e.first << ":" << e.second << " ";
	}
	cout << endl;

}