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set

Summary: All elements are automatically sorted when inserted

Set and multiset belong to associative containers, and the underlying structure is realized by binary tree

The difference between set and multiset

Set does not allow duplicate elements in the container
A multiset allows repeating elements in a container

Set constructor and assignment

Function prototype:

- set<T> st; // Default constructor

- set(const set &st); // Copy the constructor

- set operator= (const set &st); // Override the equal operator
Copy the code

“Demo” :

#include <iostream>
#include <set>

using namespace std;

void printSet(const set<int> &st)
{
    if (st.empty())
    {
        cout << "set is empty ." << endl;
    }
    else
    {
        for (set<int>::const_iterator it = st.begin(a); it ! = st.end(a); it++) { cout << *it <<"";
        }
        cout << " , size : " << st.size() << endl; }}void test01(a)
{
    set<int> st;

    st.insert(50);
    st.insert(30);
    st.insert(10);
    st.insert(20);
    st.insert(40);
    printSet(st);

    // Copy construct
    set<int> st2(st);
    printSet(st2);

    / / assignment
    set<int> st3;
    st3 = st2;
    printSet(st3);
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Summary:

The set container inserts elements with inserts
The set is automatically sorted when elements are inserted

Set size and swap

Function prototype:

- size(a);// Returns the number of elements in the container

- empty(a);// Check whether the container is empty

- swap(a);// Swap two collection containers
Copy the code

“Demo” :

#include <iostream>
#include <set>

using namespace std;

void printSet(const set<int> &st)
{
    if (st.empty())
    {
        cout << "set is empty ." << endl;
    }
    else
    {
        for (set<int>::const_iterator it = st.begin(a); it ! = st.end(a); it++) { cout << *it <<"";
        }
        cout << " , size : " << st.size() << endl; }}void test01(a)
{
    set<int> st;

    st.insert(50);
    st.insert(30);
    st.insert(10);
    st.insert(20);
    st.insert(40);

    set<int> st2;
    st2.insert(100);
    st2.insert(300);
    st2.insert(400);
    st2.insert(200);
    st2.insert(500);
    cout << "===== before swap ===== " << endl;
    cout << "set1 : ";
    printSet(st);
    cout << "set2 : ";
    printSet(st2);

    st.swap(st2);
    cout << "===== after swap ===== " << endl;
    cout << "set1 : ";
    printSet(st);
    cout << "set2 : ";
    printSet(st2);
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Set inserts and deletes elements

Function prototype:

- insert(elem); // Insert elements into the container

- clear(a);// Clear all elements

- erase(pos); // Delete the element referred to by the pos iterator and return the iterator for the next element

- erase(begin,end); // Remove the element in the [begin,end] interval and return an iterator for the next element

- erase(elem); // Remove the element with the value elem from the container
Copy the code

“Demo” :

#include <iostream>
#include <set>

using namespace std;

void printSet(const set<int> &st)
{
    if (st.empty())
    {
        cout << "set is empty ." << endl;
    }
    else
    {
        for (set<int>::const_iterator it = st.begin(a); it ! = st.end(a); it++) { cout << *it <<"";
        }
        cout << " , size : " << st.size() << endl; }}void test01(a)
{
    set<int> st;

    // Insert elements
    st.insert(50);
    st.insert(30);
    st.insert(10);
    st.insert(20);
    st.insert(40);
    printSet(st);

    // Delete elements
    st.erase(st.begin());
    printSet(st);

    // Empty the element
    st.clear(a);printSet(st);
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Set lookup and statistics

Function prototype:

- find(key); Set.end (); // Return the iterator corresponding to the key if it exists.

- count(key); // Count the number of key elements
Copy the code

“Demo” :

#include <iostream>
#include <set>

using namespace std;

void printSet(const set<int> &st)
{
    if (st.empty())
    {
        cout << "set is empty ." << endl;
    }
    else
    {
        for (set<int>::const_iterator it = st.begin(a); it ! = st.end(a); it++) { cout << *it <<"";
        }
        cout << " , size : " << st.size() << endl; }}void test01(a)
{
    set<int> st;

    // Insert elements
    st.insert(50);
    st.insert(30);
    st.insert(10);
    st.insert(20);
    st.insert(40);
    printSet(st);

    // Find elements
    set<int>::iterator pos = st.find(30);
    if(pos ! = st.end())
    {

        cout << "find " << *pos << endl;
    }
    else
    {
        cout << "not found . " << endl;
    }

    // Count elements
    int num = st.count(10);
    cout << "num = " << num << endl;
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Set is different from multiset

A set cannot insert duplicate data, whereas a multiset can
When the set inserts data, it returns the insert result, indicating whether the insert was successful
Multiset does not detect data and can insert duplicate data

“Demo” :

#include <iostream>
#include <set>

using namespace std;

// The difference between set and multiset
void test01(a)
{
    set<int> s;
    pair<set<int>::iterator, bool> ret = s.insert(10);
    if (ret.second)
    {
        cout << "Set inserted successfully for the first time" << endl;
    }
    else
    {
        cout << "Set failed to insert for the first time" << endl;
    }

    ret = s.insert(10);
    if (ret.second)
    {
        cout << "Set inserted successfully for the second time" << endl;
    }
    else
    {
        cout << "Set failed to insert second time" << endl;
    }

    multiset<int> ms;
    ms.insert(10);
    ms.insert(10);
    cout << "multiset:";
    for (multiset<int>::iterator it = ms.begin(a); it ! = ms.end(a); it++) { cout << *it <<"";
    }
    cout << endl;
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Pair group creation

Pairs of data, using pair groups can return two dataCopy the code

Function prototype:

- pair(type,type) p (value1,value2);

- pair(type,type) p = make_pair(value1,value2);
Copy the code

“Demo” :

#include <iostream>
#include <string>

using namespace std;

// Create a group
void test01(a)
{
    pair<string, int> p(string("Zhang"), 20);
    cout << "Name:" << p.first << ", age: << p.second << endl;

    pair<string, int> p2 = make_pair("Bill".22);
    cout << "Name:" << p2.first << ", age: << p2.second << endl;
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Set sort

The default collation rule of set is from small to large. You can change the collation rule by using the parafter functionCopy the code

“Demo” :

#include <iostream>
#include <set>

using namespace std;

class MyCompare
{
public:
    bool operator(a)(int v1, int v2)
    {
        returnv1 > v2; }};void test01(a)
{
    set<int> s1;
    s1.insert(19);
    s1.insert(5);
    s1.insert(10);
    s1.insert(3);

    cout << "Default order from smallest to largest:";
    for (set<int>::iterator it = s1.begin(a); it ! = s1.end(a); it++) { cout << *it <<"";
    }
    cout << endl;

    set<int, MyCompare> s2;
    s2.insert(19);
    s2.insert(5);
    s2.insert(10);
    s2.insert(3);
    cout << "Specify sort from large size:";

    for (set<int, MyCompare>::iterator it = s2.begin(a); it ! = s2.end(a); it++) { cout << *it <<"";
    }
    cout << endl;
}
int main(a)
{
    test01(a);return 0;
}
Copy the code

Set stores custom data types

For custom data types, a set must specify a collation before data can be insertedCopy the code

“Demo” :

#include <iostream>
#include <string>
#include <set>

using namespace std;

class Person
{
public:
    Person(string name, int age)
    {
        this->m_name = name;
        this->m_age = age;
    }

public:
    string m_name;
    int m_age;
};

class PersonCompare
{
public:
    bool operator(a)(const Person &p1, const Person &p2)
    {
        // In descending order of age
        returnp1.m_age > p2.m_age; }};void test01(a)
{
    Person p1("Zhang".20);
    Person p2("Bill".23);
    Person p3("Fifty".22);
    Person p4("Daisy".21);

    set<Person, PersonCompare> s;
    s.insert(p1);
    s.insert(p2);
    s.insert(p3);
    s.insert(p4);

    for (set<Person, PersonCompare>::iterator it = s.begin(a); it ! = s.end(a); it++) { cout << it->m_name <<","<< it->m_age << endl; }}int main(a)
{
    test01(a);return 0;
}
Copy the code

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【C++STL set】

set

The difference between set and multiset

Set constructor and assignment

Set size and swap

Set inserts and deletes elements

Set lookup and statistics

Set is different from multiset

Pair group creation

Set sort

Set stores custom data types

【C++STL set】

set

The difference between set and multiset

Set constructor and assignment

Set size and swap

Set inserts and deletes elements

Set lookup and statistics

Set is different from multiset

Pair group creation

Set sort

Set stores custom data types

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