Set

A set is a collection of unique elements. Searching, insertion and deletion are efficient operations on a set. We have the normal set that is ordered and also the "unordered_set" whose elements are not sorted.

File: set1.cpp

#include <iostream>
#include <set>

using namespace std ;

int main()
{
    set<char> set1 ;
    set1.insert('G');
    set1.insert('F');
    set1.insert('G');
    for (char ch1 : set1)
    {
        cout << ch1 << ' ';
    }
    cout << '\n';

    if ( set1.count( 'G' ) > 0 )
      cout << "G found in set. " << endl ;

    //another way
    if (set1.find('G') != set1.end() )
      cout << "G found in set. " << endl ;

    set1.erase( 'G' ) ;
    if (set1.find('G') == set1.end() )
      cout << "G not found in set. " << endl ;


    return 0;
}


$ g++ set1.cpp ; ./a.exe
F G
G found in set.
G found in set.
G not found in set.

A set is ordered so if we are inserting custom class objects then we need to make sure that the operator "<" is implemented. STL will determine if a set equals a custom object by the rule that for 2 objects ( obj1 and obj2 ) the objects are equal if both obj1 < obj2 and obj2 < obj1 are false.

File: set2.cpp

#include <iostream>
#include <set>

using namespace std ;

class student
{
  public:
   int id ;
   student( int idP )
    {
      id = idP ;
    }

   bool operator  <(const student& obj1 )  const
    {
       return id < obj1.id ;
    }
};


int main()
{
    set< student > set1 ;
    student  obj1(1) ;
    student  obj2(2) ;
    student  obj3(1) ;

    set1.insert(  obj1 ) ;
    set1.insert(  obj2 ) ;
    set1.insert(  obj3 ) ;

    for (student st1 : set1 )
    {
            std::cout << st1.id << ' ';
    }
   std::cout << '\n';



    return 0;
}

File: set4.cpp

#include <iostream>
#include <set>
#include <vector>
#include <list>
#include <chrono>
#include <thread>
#include <algorithm>

using namespace std ;

class Timer
{
  public:
   chrono::steady_clock::time_point start_time  ;
   chrono::steady_clock::time_point end_time ;
   void startTime()
      {
        start_time = chrono::steady_clock::now() ;
      }
   void endTime()
      {
        end_time = chrono::steady_clock::now() ;
      }
   void printTime()
      {
        chrono::milliseconds elapsed_ms =
       chrono::duration_cast<chrono::milliseconds>(end_time - start_time);

        cout << "Execution time: " << elapsed_ms.count() <<
        " milliseconds" << endl;

      }

};

//--------------------------------------------------------


//Assume vector can only contain positive numbers
void removeDuplicates1( vector<int>& v1  )
{
  set<int> set1 ;
  int left = 0 ;
    for( int x1 : v1 )
      {
        //not seen before
        if ( set1.count( x1 ) == 0 )
           {
              v1[left++] = x1 ;
           }
        else
           {

           }
          set1.insert( x1 ) ;
      } //for

      v1.resize( left ) ;

    cout << "v1:size: " << v1.size() << endl ;

}

void removeDuplicates2( vector<int>& v1  )
{
     int left = 1 ;
    // cout << "v1.size():" << v1.size() << endl ;
     for( int i1=1 ; i1 < v1.size() ; i1++ )
      {
        //not seen before
        //cout << "i1: " << i1 << " " << "v1[i1]:" << v1[i1]  << endl ;
        vector<int>::iterator it =  v1.begin() ;
        vector<int>::iterator it1 =  v1.begin() + i1 ;
        int value = v1[i1]   ;
        vector<int>::iterator it2 = find( it ,  it1, value  ) ;
        //Did not find it in the left hand side of the
        //current position
        //cout << "*it2:" << *it2 << endl ;
        if (  it2    == it1   )
           {
              // cout << "Did not find." << endl << endl ;
               v1[left++] = v1[i1] ;
           }
      } //for

      v1.resize( left ) ;

    cout << "v1:size: " << v1.size() << endl ;

}


int main()
{
    //Assume vector can only contain positive numbers
    vector<int> v1 ;
    int noElements = 100000 ;
    //int noElements = 2 ;
    Timer timerObject1 ;
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
        v1.push_back( i1 ) ;
     } //for

    timerObject1.startTime() ;
    removeDuplicates1( v1 )  ;
    timerObject1.endTime() ;
    timerObject1.printTime() ;

    v1.clear() ;
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
        v1.push_back( i1 ) ;
     } //for

    timerObject1.startTime() ;
    removeDuplicates2( v1 )  ;
    timerObject1.endTime() ;
    timerObject1.printTime() ;



    //-----------------------------------------------


    v1.clear() ;
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
     } //for
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
     } //for

    timerObject1.startTime() ;
    removeDuplicates1( v1 )  ;
    timerObject1.endTime() ;
    timerObject1.printTime() ;

    v1.clear() ;
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
     } //for
    for( int i1=1 ; i1<=noElements ; i1++ )
     {
        v1.push_back( i1 ) ;
     } //for

    timerObject1.startTime() ;
    removeDuplicates2( v1 )  ;
    timerObject1.endTime() ;
    timerObject1.printTime() ;


    return 0;
}


$ g++ set4.cpp ; ./a.exe
v1:size: 100000
Execution time: 63 milliseconds
v1:size: 100000
Execution time: 44202 milliseconds
v1:size: 100000
Execution time: 61 milliseconds
v1:size: 100000
Execution time: 29377 milliseconds

Exercise

1)

File: set_ex1.cpp

#include <iostream>
#include <set>
#include <vector>

using namespace std ;

int main()
{
    vector<int> v1 ;
    set<int> set1 ;

    v1.push_back( 4 ) ; v1.push_back( 2 ) ; v1.push_back( 4 ) ;
    v1.push_back( 1 ) ; v1.push_back( 2 ) ;
    for( int x1 : v1 )
     cout << x1 << " " ;
    cout << endl ;

    //Remove duplicates in v1 . Keep the order the same.
    //Do not use any other data structures like vector
    // other than v1 and set1 defined above.
    //Do not use nested loops. Only 1 loop




    for( int x1 : v1 )
     cout << x1 << " " ;
    cout << endl ;


    return 0;
}

File: set_ex2.cpp

#include <iostream>
#include <set>
#include <vector>

using namespace std ;
/*
  Use a single loop to determine if any 2 elements
  in the vector equal a sum value

*/
//Assume vector can only contain positive numbers
bool doesSumExistFor2Elements( vector<int>& v1 , int sum )
{


    return false ;
}


int main()
{
    //Assume vector can only contain positive numbers
    vector<int> v1 = { 3, 1, 5, 7 , 4 , 8 };

    cout << doesSumExistFor2Elements( v1, 10 ) << endl ;
    cout << doesSumExistFor2Elements( v1, 19 ) << endl ;

    vector<int> v2 = { 3, 1, 5, 7 , 4 , 2 };
    cout << doesSumExistFor2Elements( v2, 3 ) << endl  ;
    cout << doesSumExistFor2Elements( v2, 12 ) << endl  ;

    return 0;
}

File: set_ex1s.cpp


File: set_ex2s.cpp