# C++ Algorithm set_union()

C++ Algorithm set_union() function is used to find the union of two sorted ranges [first1, last1) and [first2, last2), which is formed by the elements that are present in either one of the sets or in both.

Elements are compared using operator < for the first version or using the given binary comparison function comp for the second version.

## Parameter

first1: An input iterator pointing to the first element in the first of two sorted source sequence.

last1: An input iterator pointing to the past last element in the first of two sorted source sequence.

first2: An input iterator pointing to the first element in the second sorted source sequence.

last2: An input iterator pointing to the past last element in the second sorted source sequence.

comp: A user-defined binary predicate function that accepts two arguments and returns true if the two arguments are in order and false otherwise. It follows the strict weak ordering to order the elements.

result: An output iterator addressing to the position of the first element in the destination range .

## Return value

This function returns an iterator to the end of the constructed range.

## Complexity

Complexity is linear in the distance between [first1, last1) and [first2, last2): performs up to 2*(count1+count2)-1 comparisons. Where count1 = last1- first1 and count2 = last2- first2.

## Data races

The object in the range [first1, last1) and [first2. last2) are accessed.

The object in the range between result and returned value are modified.

## Exceptions

This function throws an exception if any of element comparison, the element assignments or an operation on iterator throws an exception.

## Example 1

Let's see the simple example to demonstrate the use of set_union():

Output:

```1
2
3
4
5
6
```

## Example 2

Let's see another simple example:

Output:

```First array contains: 5 10 15 20 25
Second array contains: 50 40 30 20 10

The union has 8 elements:
5 10 15 20 25 30 40 50
```

## Example 3

Let's see another simple example to find the list of all students who are attending both subjects:

Output:

```Students in first subject: Nikita Divya Deep Kashish
Students in second subject: Aman Nikita Amita Deep

Students attending both subjects are:
Aman Amita Deep Divya Kashish Nikita
```

## Example 4

Let's see a simple example:

Output:

```A B C D E F
```

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