A set is an associative container available in the C++ Standard Template Library(STL) that is used for unique elements in a specific order, it internally uses the working principle of a Binary Search Tree to store elements.

Different Ways to Initialize a set in C++: 

1. Initialization using the default constructor.
2. Initialization using initializer list.
3. Initialization using an array.
4. Initialization using a vector.
5. Initialization from another set using the copy constructor.
6. Initialization from another iterable data structure using range constructor.

1. Initialization Using the Default Constructor

One standard way to initialize a set is to initialize using the default constructor, this will generate an empty set. Elements can be added to it using an inbuilt set.insert() method.

Syntax:

set<int>New_set;
New_set.insert(element1)

Here, the insert() method can be further used to insert elements into the set.

Below is the C++ program to implement the above approach:

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Time Complexity : O(N logN)

Auxiliary Space : O(N)

2. Initialization using an Initializer List

Another way of initialization is to pass a predefined list of elements (initializer_list) as an argument to the default constructor of the set as shown below:

Syntax:

set<int>New_set({element1, element2, element3, element4});

Below is the C++ program to implement the above approach:

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3. Initialization Using an Array

The elements can be added to the set using an array of the same data type.

Syntax:

set<int>New_set(old_arr, old_arr + n); 

Here, old_arr is the array of integers from which contents will be copied into the New_set.

Below is the C++ program to implement the above approach:

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4. Initialization Using a Vector

One can store the elements to the set using a vector of the same data type.

Syntax:

set<int>New_set(old_vector.begin(),old_vector.end()); 

Here, old_vector is the vector of integers from which contents will be copied into the New_set.

Below is the C++ program to implement the above approach:

Table
Cement
Floor
Grass
Ground

5. Initialization From Another Set Using the Copy Constructor

One way to initialize a set is to copy contents from another set one after another by using the copy constructor.

Syntax:

set<int>New_set(old_set);

Here, old_set is the set from which contents will be copied into the New_set

Below is the C++ program to implement the above approach:

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6. Initialization From Another Iterable Data Structure Using Range Constructor

Another way to initialize a set is to use a range constructor to copy elements from an iterable data structure to the newly initialized set.

Syntax:

set<int>New_set(begin(old_set), end(old_set));

Here, old_set is the set from which contents will be copied into the New_set.

Below is the C++ program to implement the above approach:

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