How to use the set_intersection() function in C++

In this shot, we will learn how to use the set_intersection() function in C++.

The set_intersection() function is available in the <algorithm> library in C++.

The set_intersection() function is used to find the intersection of the two sorted ranges, which is formed only by the common elements between the sets.

Syntax

The syntax of the set_intersection() function is shown below:

OutputIterator set_intersection(first1, last1, first2, last2, res)

Parameters

The set_intersection() method takes the following parameters:

First1: The input iterator to the initial position of the first sorted sequence.
Last1: The input iterator to the final position of the first sorted sequence.
First2: The input iterator to the initial position of the second sorted sequence.
Last2: The input iterator to the final position of the second sorted sequence.
Res: The output iterator to the initial position of the range where the resulting sequence is stored.

Returns

The set_intersection() returns an iterator to the end of the constructed range.

Code

Let’s have a look at the code now.

#include <algorithm> 
#include <iostream> 
#include <vector> 
using namespace std;
int main()
{
  int first[] = { 25, 110, 105, 120, 125 };
  int second[] = { 150, 120, 105, 225, 25 };
  int n = sizeof(first) / sizeof(first[0]);
  cout << "First array contains :";
  for (int i = 0; i < n; i++)
    cout << " " << first[i];
  cout << "\n";
  cout << "Second array contains :";
  for (int i = 0; i < n; i++)
    cout << " " << second[i];
  cout << "\n\n";
  vector<int> vec(10);
  vector<int>::iterator it1, st1;
  sort(first, first + n);
  sort(second, second + n);
  it1 = set_intersection(first, first + n, second, second + n, vec.begin());
  cout << "The intersection has " << (it1 - vec.begin())<< " elements:\n";
  for (st1 = vec.begin(); st1 != it1; ++st1)
    cout << ' ' << *st1;
  cout << '\n';
  return 0;
}

Explanation:

In lines 1 to 3, we imported the required header files.
In line 6, we made a main() function.
In line 9 and 10, we initialized two arrays.
From lines 13 to 15, we displayed the elements of the first array.
From lines 18 to 20, we displayed the elements of the second array.
In line 23, we declared a vector of int type.
In line 24, we declared two iterators to a vector of int type.
In lines 26 and 27, we sorted the two arrays.
In line 29, we used the set_intersection() function to obtain the intersection and store the output vector’s initial position in the iterator.
In line 31, we displayed the number of elements in the intersection.
In lines 32 and 33, we displayed the elements of intersection using the iterator and loop.

So, this is how to use the set_intersection() function in C++.

Free Resources

License: Creative Commons-Attribution-ShareAlike 4.0 (CC-BY-SA 4.0)