std::set and std::map are STL containers that implements Self-Balancing BST.

If std::set store a single value (key), std::map store a pair of value (key and value).

This module Will explains on how to use both STL containers.

• set::empty()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int> s;
  
      if(s.empty()){
          cout << "This set is empty" << endl;
      }
  
      return 0;
  }

• set::insert()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int> s;
  
      s.insert(4);
      s.insert(3);
      s.insert(2);
      s.insert(1);
  
      for(auto i = s.begin(); i != s.end(); i++){
          cout << *i << endl;
      }
  
      return 0;
  }

  std::set will automatically sort the data ascendingly. To sort decendingly, use function rbegin() and rend() or have a look on example below.

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int, greater<int>> s;
  
      s.insert(4);
      s.insert(3);
      s.insert(2);
      s.insert(1);
  
      for(auto i = s.begin(); i != s.end(); i++){
          cout << *i << endl;
      }
  
      return 0;
  }

  note: std::set couldn't store duplicate values

• set::find()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int> s;
  
      s.insert(4);
      s.insert(3);
      s.insert(2);
      s.insert(1);
  
      auto pointer = s.find(5);
  
      if(pointer == s.end()){
          cout << "data not found" << endl;
      }
      else{
          cout << "data found" << endl;
      }
  
      return 0;
  }

• set::erase()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int> s;
  
      s.insert(4);
      s.insert(3);
      s.insert(2);
      s.insert(1);
  
      s.erase(2);
      // doesn't use iterator
  
      for(auto i = s.begin(); i != s.end(); i++){
          cout << *i << endl;
      }
  
      return 0;
  }

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      set<int> s;
  
      s.insert(4);
      s.insert(3);
      s.insert(2);
      s.insert(1);
  
      auto pointer = s.find(2);
  
      s.erase(pointer);
      // using iterator
  
      for(auto i = s.begin(); i != s.end(); i++){
          cout << *i << endl;
      }
  
      return 0;
  }

More on std::set could be read here or on C++ Language Documentation here.

• map::empty()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      map<int, int> m;
  
      if(m.empty()){
          cout << "this map is empty" << endl;
      }
  
      return 0;
  }

• map::insert()

  There are a lot of ways to insert values on std::map.

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      map<int, int> m;
      
      m.insert({1, 2});
      // directly
  
      m.insert(make_pair(2, 3));
      // use function make_pair
  
      m.insert(pair<int, int>(3, 4));
      // create pair object, similar to the example before
  
      m[4] = 5;
      // use indexing
  
      m[5]++;
      // increment
  
      for(auto i = m.begin(); i != m.end(); i++){
          cout << i->first << " " << i->second << endl;
      }
  
      return 0;
  }

  How to sort key on std::map descendingly?

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      map<int, int, greater<int>> m;
      
      m.insert({1, 2});
      m.insert(make_pair(2, 3));
      m.insert(pair<int, int>(3, 4));
      m[4] = 5;
      m[5]++;
  
      for(auto i = m.begin(); i != m.end(); i++){
          cout << i->first << " " << i->second << endl;
      }
  
      return 0;
  }

• map::find()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      map<int, int> m;
  
      m.insert({1, 2});
      m.insert(make_pair(2, 3));
      m.insert(pair<int, int>(3, 4));
      m[4] = 5;
      m[5]++;
  
      auto pointer = m.find(1);
      /* 
      using function find
      return an iterator that points to an element with
      key = 1
      */
      if(pointer != m.end()){
          cout << pointer->first << " " << pointer->second << endl;
      }
  
      cout << m[5] << endl;
      /* 
      indexing, only shows the value of element with
      key = 5
      */
  
      return 0;
  }

• map::erase()

  #include <bits/stdc++.h>
  using namespace std;
  
  int main(){
      map<int, int> m;
  
      m.insert({1, 2});
      m.insert(make_pair(2, 3));
      m.insert(pair<int, int>(3, 4));
      m[4] = 5;
      m[5]++;
      m[6] = 6;
  
      m.erase(1);
      // erase an element with key = 1
  
      auto pointer1 = m.find(2);
      m.erase(pointer1);
      // using iterator from function find
  
      auto pointer2 = m.find(5);
      m.erase(m.begin(), pointer2);
      // erase all element with key < 5
  
      m[5] = 0;
      /*
      not really erasing, only change value to 0
      on element with key = 5
      */
  
      for(auto i = m.begin(); i != m.end(); i++){
          cout << i->first << " " << i->second << endl;
      }
  
      return 0;
  }

More on std::map could be read here or on C++ Language Documentation here.