Merge operations using STL in C++ | merge(), includes(), set_union(), set_intersection(), set_difference(), ., inplace_merge,

Difficulty Level : Easy
Last Updated : 19 Jan, 2018

Some of the merge operation classes are provided in C++ STL under the header file “algorithm”, which facilitates several merge operations in a easy manner.
Some of them are mentioned below.

merge(beg1, end1, beg2, end2, beg3) :- This function merges two sorted containers and stores in new container in sorted order (merge sort). It takes 5 arguments, first and last iterator of 1st container, first and last iterator of 2nd container and 1st iterator of resultant container.

includes(beg1, end1, beg2, end2) :- This function is used to check whether one sorted container elements are including other sorted container elements or not. Returns true if 1st container includes 2nd container else returns false.

// C++ code to demonstrate the working of 
// merge() and include()
#include<iostream>
#include<algorithm> // merge operations
#include<vector> // for vector
using namespace std;
int main()
{
 // Initializing 1st vector
 vector<int> v1 = {1, 3, 4, 5, 20, 30};
      
 // Initializing 2nd vector
 vector<int> v2 = {1, 5, 6, 7, 25, 30};
      
 // Declaring resultant vector
 // for mergeing
 vector<int> v3(12);
      
 // Using merge() to merge vectors v1 and v2
 // and storing result in v3
 merge(v1.begin(), v1.end(), v2.begin(), 
                   v2.end(), v3.begin());
      
 // Displaying resultant container
 cout << "The new container after merging is :\n";
 for (int &x : v3) 
     cout << x << " ";
 cout << endl;
   
 // Initializing new vector
 vector<int> v4 = {1, 3, 4, 5, 6, 20, 25, 30};
   
 // Using include() to check if v4 contains v1
 includes(v4.begin(), v4.end(), v1.begin(), v1.end())?
        cout << "v4 includes v1":
        cout << "v4 does'nt include v1";
   
 return 0;    
}

Output

The new container after merging is :
1 1 3 4 5 5 6 7 20 25 30 30 
v4 includes v1

inplace_merge(beg1, beg2, end) :- This function is used to sort two consecutively placed sorted ranges in a single container. It takes 3 arguments, iterator to beginning of 1st sorted range, iterator to beginning of 2nd sorted range, and iterator to last position.

// C++ code to demonstrate the working of 
// inplace_merge()
#include<iostream>
#include<algorithm> // merge operations
#include<vector> // for vector
using namespace std;
int main()
{
   
 // Initializing 1st vector
 vector<int> v1 = {1, 3, 4, 5, 20, 30};
      
 // Initializing 2nd vector
 vector<int> v2 = {1, 5, 6, 7, 25, 30};
      
 // Declaring resultant vector
 // for inplace_merge()
 vector<int> v3(12);
   
 // using copy to copy both vectors into 
 // one container
 auto it = copy(v1.begin(), v1.end(), v3.begin());
 copy(v2.begin(), v2.end(), it);
   
 // Using inplace_merge() to sort the container
 inplace_merge(v3.begin(),it,v3.end());
      
 // Displaying resultant container
 cout << "The new container after inplace_merging is :\n";
 for (int &x : v3) 
     cout << x << " ";
 cout << endl;
  
 return 0;
      
}

Output:

The new container after inplace_merging is :
1 1 3 4 5 5 6 7 20 25 30 30

set_union(beg1, end1, beg2, end2, beg3) :- This function computes the set union of two containers and stores in new container .It returns the iterator to the last element of resultant container. It takes 5 arguments, first and last iterator of 1st container, first and last iterator of 2nd container and 1st iterator of resultant container . The containers should be sorted and it is necessary that new container is resized to suitable size.

set_intersection(beg1, end1, beg2, end2, beg3) :- This function computes the set intersection of two containers and stores in new container .It returns the iterator to the last element of resultant container. It takes 5 arguments, first and last iterator of 1st container, first and last iterator of 2nd container and 1st iterator of resultant container . The containers should be sorted and it is necessary that new container is resized to suitable size.
One way to implement set-union and set-intersection in sorted ranges can be found here

// C++ code to demonstrate the working of 
// set_union() and set_intersection()
#include<iostream>
#include<algorithm> // for merge operations
#include<vector> // for vector
using namespace std;
int main()
{
 // Initializing 1st vector
 vector<int> v1 = {1, 3, 4, 5, 20, 30};
      
 // Initializing 2nd vector
 vector<int> v2 = {1, 5, 6, 7, 25, 30};
      
 // Declaring resultant vector
 // for union
 vector<int> v3(10);
      
 // Declaring resultant vector
 // for intersection
 vector<int> v4(10);
      
 // using set_union() to compute union  of 2 
 // containers v1 and v2 and store result in v3
 auto it = set_union(v1.begin(), v1.end(), v2.begin(), 
                              v2.end(), v3.begin());
      
 // using set_intersection() to compute intersection
 // of 2 containers v1 and v2 and store result in v4
 auto it1 = set_intersection(v1.begin(),v1.end(), 
               v2.begin(), v2.end(), v4.begin());
      
 // resizing new container
 v3.resize(it - v3.begin());
      
 // resizing new container
 v4.resize(it1 - v4.begin());
      
 // Displaying set union
 cout << "Union of two containers is : ";
 for (int &x : v3) 
     cout << x << " ";
 cout << endl;
      
 // Displaying set intersection
 cout << "Intersection of two containers is : ";
 for (int &x : v4) 
     cout << x << " ";
 cout << endl;
      
 return 0;    
}

Output:

Union of two containers is : 1 3 4 5 6 7 20 25 30 
Intersection of two containers is : 1 5 30

set_difference(beg1, end1, beg2, end2, beg3) :- This function computes the set difference of two containers and stores in new container .It returns the iterator to the last element of resultant container. It takes 5 arguments, first and last iterator of 1st container, first and last iterator of 2nd container and 1st iterator of resultant container . The containers should be sorted and it is necessary that new container is resized to suitable size.

set_symmetric_difference(beg1, end1, beg2, end2, beg3) :- This function computes the set symmetric difference of two containers and stores in new container .It returns the iterator to the last element of resultant container. It takes 5 arguments, first and last iterator of 1st container, first and last iterator of 2nd container and 1st iterator of resultant container . The containers should be sorted and it is necessary that new container is resized to suitable size.

// C++ code to demonstrate the working of 
// set_difference() and set_symmetric_difference()
#include<iostream>
#include<algorithm> // for merge operations
#include<vector> // for vector
using namespace std;
int main()
{
 // Initializing 1st vector
 vector<int> v1 = {1, 3, 4, 5, 20, 30};
      
 // Initializing 2nd vector
 vector<int> v2 = {1, 5, 6, 7, 25, 30};
      
 // Declaring resultant vector
 // for difference
 vector<int> v3(10);
      
 // Declaring resultant vector
 // for symmetric_difference
 vector<int> v4(10);
      
      
 // using set_difference() to compute difference
 // of 2 containers v1 and v2.
 auto it = set_difference(v1.begin(), v1.end(),
              v2.begin(), v2.end(), v3.begin());
      
 // using set_symmetric_difference() to compute 
 // symmetric_difference/ of 2 containers
 auto it1 = set_symmetric_difference(v1.begin(), 
       v1.end(), v2.begin(), v2.end(), v4.begin());
      
 // resizing new container
 v3.resize(it - v3.begin());
      
 // resizing new container
 v4.resize(it1 - v4.begin());
      
 // Displaying set difference
 cout << "Difference of two containers is : ";
 for (int &x : v3) 
     cout << x << " ";
 cout << endl;
      
 // Displaying set symmetric_difference
 cout << "symmetric_difference of two containers is : ";
 for (int &x : v4) 
     cout << x << " ";
 cout << endl;
      
 return 0;    
}

Output:

Difference of two containers is : 3 4 20 
Symmetric difference of two containers is : 3 4 6 7 20 25

This article is contributed by Manjeet Singh .If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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