Detailed explanation of the usage examples of map and set in C++

template < class T,                        // set::key_type/value_type
           class Compare = less<T>,        // set::key_compare/value_compare
           class Alloc = allocator<T>      // set::allocator_type
           > class set;

//empty (1) Default construct without parametersexplicit set(const key_compare& comp = key_compare(),
	 const allocator_type& alloc = allocator_type());
// range (2) Iterator interval constructiontemplate <class InputIterator>
set(InputIterator first, InputIterator last,
	const key_compare& comp = key_compare(),
	const allocator_type & = allocator_type());
// copy (3) copy constructset (const set& x);
// initializer list (5) initializer list constructionset (initializer_list<value_type> il,
 const key_compare& comp = key_compare(),
 const allocator_type& alloc = allocator_type());

// Iterator is a bidirectional iteratoriterator -> a bidirectional iterator to const value_type
// Forward iteratoriterator begin();
iterator end();
// Reverse iteratorreverse_iterator rbegin();
reverse_iterator rend();

#include <iostream>
#include <set>
using namespace std;
int main()
{
	//Deduplication + ascending order sort	set<int> s;
	//Deduplication + descending order, give a simulated function greater than	//set<int, greater<int>> s;
	//set<int, greater<int>> s = {1,2,7,4,9,6,}; initializer_list initialization	(2);
	(1);
	(5);
	(6);
	//set&lt;int&gt; iterator it =  ();
	auto it = ();
	while (it != ())
	{
		//*it = 1; the value inside cannot be modified		cout &lt;&lt; *it &lt;&lt; " ";
		it++;
	}
	cout &lt;&lt; endl;
	//Insert a value of initializer_list, if it already exists, the insertion fails	({1,5,3,2,7,9});
	for (auto e : s)
	{
		cout &lt;&lt; e &lt;&lt; " ";
	}
	cout &lt;&lt; endl;
	//Insert string class object, the comparison of string class object is based on the ascll code to compare the size.	set&lt;string&gt; strset = {"sort","add","insert"};
	for (auto &amp;e : strset)
	{
		cout &lt;&lt; e &lt;&lt; " ";
	}
	cout &lt;&lt; endl;
	return 0;
}

int main()
{
	set<int> s = {2,7,4,3,1,9,5,0};
	for (auto& e : s)
	{
		cout << e << " ";
	}
	cout << endl;
	//Delete the minimum value	(());
	for (auto& e : s)
	{
		cout << e << " ";
	}
	cout << endl;
	//Delete the input value, this value may or may not be there	int x;
	cin >> x;
	int num = (x);
	if (num == 0)
	{
		cout << x  << "Not exists!" << endl;
	}
	for (auto& e : s)
	{
		cout << e << " ";
	}
	cout << endl;
	//Search directly, and then use the iterator to delete	cin >> x;
	auto pos = (x);
	if (pos != ())
	{
		(pos);
	}
	else
	{
		cout << x << "Not exists" << endl;
	}
	for (auto& e : s)
	{
		cout << e << " ";
	}
	cout << endl;
	//Lookup O(n) in the algorithm library will not be used like this	auto pos1 = find((), (), x);
	//Set's own implementation of search O(logn)	auto pos2 = (x);
	//Use cout to quickly realize indirect search	cin >> x;
	if ((x))
	{
		cout << x << "exist!" << endl;
	}
	else
	{
		cout << x << "Not exists!" << endl;
	}
	return 0;
}

int main()
{
	set<int> myset;
	for (int i = 1; i < 10; i++)
	{
		(i * 10);//10 20 30 40 50 60 70 80 90
	}
	for (auto e : myset)
	{
		cout << e << " ";
	}
	cout << endl;
	//The [itlow,itup] found in the implementation contains the [30,60] interval	//Return>=30	auto itlow = myset.lower_bound(30);
	//Return>60	auto itup = myset.upper_bound(60);
	//Delete the value of this interval	(itlow,itup);
	for (auto e : myset)
	{
		cout << e << " ";
	}
	cout << endl;
	return 0;
}

int main()
{
	multiset<int> s = {4,6,4,3,6,7,8,9,2,5,3,7,8,9};
	auto it = ();
	while (it != ())
	{
		cout << *it << " ";
		++it;
	}
	cout << endl;
	// Compared to set, there may be multiple x, and find is the first in the middle order.	int x;
	cin >> x;
	auto pos = (x);
	while (pos != () && *pos == x)
	{
		cout << *pos << " ";
		++pos;
	}
	cout << endl;
	//The difference compared to set is that count will return the actual number of x	cout << (x) << endl;
	//The difference compared to set is that erase will delete all x in it	(x);
	for (auto e : s)
	{
		cout << e << " ";
	}
	cout << endl;
	return 0;
}

class Solution {
public:
    vector<int> intersection(vector<int>& nums1, vector<int>& nums2) {
        // Here we use set to implement sorting + deregulating arrays        set<int> s1((),());//Initialize with a segment of iterator interval        set<int> s2((),());
        // Small ++, equality means intersection        vector<int> ret;
        auto it1 = ();
        auto it2 = ();
        while(it1 != () && it2 != ())
        {
            if(*it1 < *it2) it1++;
            else if (*it1 > *it2) it2++;
            else 
            {
                ret.push_back(*it1);
                it1++;
                it2++;
            }
        }
        return ret;
    }
};

class Solution {
public:
    ListNode *detectCycle(ListNode *head) {
        set<ListNode*> s;
        ListNode* cur = head;
        while(cur)
        {
            if((cur))
                return cur;//Equal to 1 is the entry point            else
                (cur);
            cur = cur -> next;
        }
        return nullptr;
    }
};

template < class Key, // map::key_type
 class T, // map::mapped_type
 class Compare = less<Key>, // map::key_compare
 class Alloc = allocator<pair<const Key,T> > // 
map::allocator_type
 > class map

typedef pair<const Key, T> value_type;
template <class T1, class T2>
struct pair
{
	typedef T1 first_type;
	typedef T2 second_type;
	T1 first;
	T2 second;
	pair() : first(T1()), second(T2())
	{}
	pair(const T1& a, const T2& b) : first(a), second(b)
	{}
	template<class U, class V>
	pair(const pair<U, V>& pr) : first(), second()
	{}
};
template <class T1, class T2>
inline pair<T1, T2> make_pair(T1 x, T2 y)
{
	return (pair<T1, T2>(x, y));
}

// empty (1) Default construct without parametersexplicit map (const key_compare& comp = key_compare(),
 const allocator_type& alloc = allocator_type());
// range (2) Iterator interval constructiontemplate <class InputIterator>
 map (InputIterator first, InputIterator last,
 const key_compare& comp = key_compare(),
 const allocator_type& = allocator_type());
// copy (3) copy constructmap (const map& x);
// initializer list (5) initializer list constructionmap (initializer_list<value_type> il,
 const key_compare& comp = key_compare(),
 const allocator_type& alloc = allocator_type());
// Iterator is a bidirectional iteratoriterator -> a bidirectional iterator to const value_type
// Forward iteratoriterator begin();
iterator end();
// Reverse iteratorreverse_iterator rbegin();
reverse_iterator rend();

Member types
key_type->The first template parameter(Key)
mapped_type->The second template parameter(T)
value_type->pair<const key_type, mapped_type>
// Insert a single data, if the key already exists, the insertion fails. If the key exists equal value and is not equal, the insertion fails.pair<iterator, bool> insert(const value_type& val);
// List insertion, values ​​that already exist in the container will not be insertedvoid insert(initializer_list<value_type> il);
// Iterator interval is inserted, and values ​​that already exist in the container will not be insertedtemplate <class InputIterator>
void insert(InputIterator first, InputIterator last);
// Find k, return the iterator where k is located, and return end() is not founditerator find(const key_type& k);
// Find k and return the number of ksize_type count(const key_type& k) const;
// Delete the value of the position of an iteratoriterator erase(const_iterator position);
// Delete k, k exists and returns 0, and exists and returns 1size_type erase(const key_type& k);
// Delete the value of an iterator intervaliterator erase(const_iterator first, const_iterator last);
// Returns an iterator with positions greater than or equal kiterator lower_bound(const key_type& k);
// Returns an iterator greater than k positionconst_iterator lower_bound(const key_type& k) const;

Member types
key_type->The first template parameter(Key)
mapped_type->The second template parameter(T)
value_type->pair<const key_type, mapped_type>
// Find k and return the iterator where k is located. If it is not found, return end(). If it is found, the mapped_type value corresponding to the key can be modified through the iterator.iterator find(const key_type& k);
// Description of insert return value in the document// The single element versions (1) return a pair, with its member pair::first set to an iterator pointing to either the newly inserted element or to theelement with an equivalent key in the  pair::second element in the pairis set to true if a new element was inserted or false if an equivalent keyalready existed.
// insert an insert object// 1. If the key is already in the map and the insertion fails, a pair<iterator,bool> object is returned, and the pair object first is the iterator of the node where the key is located, and second is false// 2. If the key is not in the map and the insertion is successful, a pair<iterator,bool> object is returned, and the pair object first is the iterator of the newly inserted key node, second is true// In other words, no matter whether the insertion is successful or failed, the first return to the pair<iterator, bool> object will point to the iterator where the key is located// This means that insert acts as a search function when insert fails. It is precisely because of this that insert can be used to implement it.operator[]
// It should be noted that there are two pairs here, so don't confuse it. One is the pair<key, T> stored in the red tree node at the bottom of the map, and the other is the insert return value pair<iterator, bool>pair&lt;iterator, bool&gt; insert(const value_type &amp; val);
mapped_type&amp; operator[] (const key_type&amp; k);
// Internal implementation of operatormapped_type&amp; operator[] (const key_type&amp; k)
{
	// 1. If k is not in the map, insert will insert the default values ​​of k and mapped_type (the default value is constructed with the default construction), and at the same time [] returns a reference to the mapped_type value stored in the node, then we can modify the return mapped value through reference.  So[] has the insert + modification function		// 2. If k is in map, insert will fail, but insert returns the first of the pair object, which is an iterator pointing to the key node. The return value is also [] and the reference to the mapped_type value is stored in the node, so [] has the function of search + modification		pair&lt;iterator, bool&gt; ret = insert({ k, mapped_type() });
	iterator it = ;
	return it-&gt;second;
}

#include <map>
int main()
{
	pair<string, string> kv1 = {"left","left"};
	//Initializer_list construction and iterative traversal	map<string, string> dict = { {"left","left"},{"right","right"},{"insert","insert"},{"erase","delete"}};
	map<string, string>::iterator it = ();
	while (it != ())
	{
		//cout << *it << " "; //pair does not support stream extraction and stream insertion, it is a structure		//cout &lt;&lt; (*it).first &lt;&lt; ":" &lt;&lt; (*it).second &lt;&lt; endl;;
		cout &lt;&lt; it-&gt;first &lt;&lt; ":" &lt;&lt; it-&gt;second &lt;&lt; endl;
		//cout << ->()->first << ":" << ->()->second << endl;//Native writing		++it;
	}
	// Map insertion	//The four ways to insert the pair, the last one is the most convenient way to compare	pair&lt;string, string&gt; kv2("first","First");
	(kv2);
	//Anonymous object	(pair&lt;string, string&gt;("second", "Second"));
	//make_pair
	(make_pair("sort","Sorting"));//make_pair is a function template. You don’t need to declare template parameters. You can deduce it yourself. Construct a pair object at the bottom and then return it.	//The last one is best	({"auto","Automatic"});//Support implicit type conversion	//Support scope for traversal	for (auto&amp; e : dict)
	{
		cout &lt;&lt;  &lt;&lt; ":" &lt;&lt;  &lt;&lt; endl;
	}
	cout &lt;&lt; endl;
	//Structured binding C++17	//for (const auto&amp; [k,v] : dict)
	//{
	//	cout &lt;&lt; k &lt;&lt; ":" &lt;&lt; v &lt;&lt; endl;
	//}
	string str;
	while (cin &gt;&gt; str)
	{
		auto ret = (str);
		if (ret != ())
		{
			cout &lt;&lt; "-&gt;" &lt;&lt; ret-&gt;second &lt;&lt; endl;
		}
		else
		{
			cout &lt;&lt; "If there is no such word, please re-enter" &lt;&lt; endl;
		}
	}
	//First cannot be modified, but second can be modified	return 0;
}

#include <iostream>
#include <string>
#include <map>
using namespace std;
int main()
{
	//Count the number of times fruit appears	string arr[] = { "apple", "watermelon", "apple", "watermelon", "apple", "apple", "watermelon","apple", "banana", "apple", "banana" };
	map<string, int> countMap;
	//First find out if the fruit is in the map	//1. Not present, indicating that the fruit appears for the first time, then insert the fruit {fruit, 1}	//2. In, the corresponding number of times the fruit found is +1	for (const auto& str : arr)
	{
		auto ret = (str);
		if (ret == ())//Then it proves that		{
			({str,1});
		}
		// Otherwise, in		else
		{
			ret->second++;
		}
	}
	//countMap[str]++; The second way to write	for (const auto& e : countMap)
	{
		cout <<  << ":" <<  << endl;
	}
	cout << endl;
	return 0;
}

class Solution {
public:
    Node* copyRandomList(Node* head) {
        map<Node*,Node*> nodeMap;
        Node* copyhead = nullptr,*copytail = nullptr;//Define one head and one tail        Node* cur = head;
        while(cur)
        {
            //If empty            if(copytail == nullptr)
            {
                copyhead = copytail = new Node(cur->val);
            }
            //If not empty            else
            {
                copytail->next = new Node(cur->val);
                copytail = copytail->next;
            }
            //Let the original node and copy node establish map            nodeMap[cur] = copytail;
            cur = cur->next;
        }
        //Processing random        cur = head;
        Node* copy = copyhead;
        while(cur)
        {
            //The random of the original linked list is empty, and the random of the copy linked list is also empty            if(cur->random == nullptr)
            {
                copy->random = nullptr;
            }
            else
            {
                copy->random = nodeMap[cur->random];
            }
            cur = cur->next;
            copy = copy->next;
        }
        return copyhead;
    }
};

class Solution {
public:
    struct Compare
    {
        bool operator()(const pair<string,int>& kv1,const pair<string,int>& kv2)
        {
            return  > ;
        }
    }; 
    vector<string> topKFrequent(vector<string>& words, int k) {
        //Statistics        map<string,int> countMap;
        for(auto &str : words)
        {
            countMap[str]++;
        }
        vector<pair<string,int>> v((),());//Iterator interval initialization        stable_sort((),(),Compare());
        vector<string> retv;
        for(size_t i = 0; i < k ; ++i)
        {
            retv.push_back(v[i].first);//What you take is the word in each pair object        }
        return retv;
    }
};

class Solution {
public:
	struct Compare
	{
		bool operator()(const pair<string, int>& x, const pair<string, int>& y)
		{
			return  >  || ( ==  &&  < );;
		}
	};
	vector<string> topKFrequent(vector<string>& words, int k) 
	{
		map<string, int> countMap;
		for (auto& e : words)
		{
			countMap[e]++;
		}
		vector<pair<string, int>> v((), ());
		// Descending function controls descending order, functor controls equal times, and the dictionary order is in front		sort((), (), Compare());
		// Take the first k		vector<string> strV;
		for (int i = 0; i < k; ++i)
		{
			strV.push_back(v[i].first);
		}
		return strV;
	}
};

class Solution {
public:
	struct Compare
	{
		bool operator()(const pair<string, int>& x, const pair<string, int>& y)
			const
		{
			// Note that the bottom layer of the priority queue is inverse, and the heap must be implemented less than comparison, so the number of times is equal. If you want a small dictionary order, you must compare the large dictionary order before the first one is true				return  <  || ( ==  &&  > );
		}
	};
	vector<string> topKFrequent(vector<string>& words, int k)
	{
		map<string, int> countMap;
		for (auto& e : words)
		{
			countMap[e]++;
		}
		// Put the <word, number of times> in the map into priority_queue, and the functor controls the heap, and the number of times is the same, sorted according to the dictionary order rules.			priority_queue&lt;pair&lt;string, int&gt;, vector&lt;pair&lt;string, int&gt;&gt;, Compare&gt;p((), ());
		vector&lt;string&gt; strV;
		for (int i = 0; i &lt; k; ++i)
		{
			strV.push_back(().first);
			();
		}
		return strV;
	}