Sets in C++

Set in C++ :

STL in C++ are of great use when it comes to competitive programming. So here were are going to have look at the set stl. This post is based on what I learned about set and I have tried in simple english.


How to declare a map :

First include the header file #include

then you are ready to go with your map!!!

set<int> s;

To clear the set : 
     
      We can clear the function using clear() function.

s.clear();

To insert into the set :

      We can insert into a using insert() function.

s.insert(10);

To find whether an element exists in the set :

       We have to use find() function to check whether an element is present if it equals s.end()  element is not there in set.

cout<<s.find(10)==s.end();//prints 0 if 10 is not there

To erase an element in the set :

      Remember clear deletes the entire set whereas erase() function deletes just one element.

s.erase(10);

Map in C++ :

STL in C++ are of great use when it comes to competitive programming. So here were are going to have look at the map stl. This post is based on what I learned about maps and I have tried in simple english.


How to declare a map :

First include the header file #include <map>

then you are ready to go with your map!!!

Declaration syntax : map<type,type> name;

Examples : 

1. map<string,int> a;
2. map<int,int> b;
3. map<char,int> mymap;

How to insert into the map :

 You can simply insert like arrays for example

map<string,int> a; 

a["hello"]=2;

Or else you can use the insert function of map like as follows :

 map<string,int> a;

a.insert(pair<char,int>("a",10));

How to iterate through all the values in map :

we have to create a map iterator and use begin() and end() functions to iterate through the map,.

map<string,int> a;

a["hello"]=2;

a["hi"]=3; 

map<string,int>::iterator it; 

for(it=a.begin();it!=a.end();it++) 

cout<<it->first<<" "<<it->second;

How to delete a value in map :

We can use erase()  function to delete any values as follows :

a.erase("hello"); 

How to find whether a value is there are not :

we can use find() or count() method to find whether a key is there are not.

using count() method :

if(a.count(key))

//key exists

using find() method :

                                                     cout<<a.find(key)->second; 

find() returns 0 if there is no such key otherwise it prints the key's value.

How to print map in reverse order :

 we can use reverse iterator function to print the map in reverse order as follows

std::map<string,int>::reverse_iterator it;

for(it=m.rbegin();it!=r.rend();it++)

cout<<it->second<<" ";