set::insert() function in C++ STL

The std::set::insert() is a built-in function of C++ STL set container which is used to insert new elements in it. In this article, we will learn how to use set::insert() function in our C++ programs.

Syntax

The string::replace() function provides 6 different overloads for different purposes:

st.insert(val);
st.insert(pos, val);
st.insert({ val1,val2,....});
st.insert(first, last);

Following are the different ways in which we can insert elements in an std::set container using set::insert() method:

Insert a Single Element

We can use the set::insert() to insert a single in the set. It will be inserted at the position according to the order of the set elements.

Syntax

st.insert(val)

Parameters

• val: Value which we have to insert.

Return Value

• The version of the function returns a pair, where pair::first is an iterator pointing to either the newly inserted element or to the element with an equivalent value in the set.
  The pair::second element is a boolean value that tells whether the element was successfully inserted or not.

Note: As set contains only unique values, set::insert() function won't insert the elements that is already present in the set.

Example

// C++ program to illustrate how to insert a // single element using set::insert() #include <bits/stdc++.h> using namespace std; int main() {  set<int> st;  // Inserting an element  st.insert(23);    // Inserting more elements  st.insert(67);  st.insert(2);  st.insert(11);  for (auto i : st)  cout << i << " ";  return 0; } 

2 11 23 67 

Time Complexity: O(log n), where n is the number of elements already present in the set.
Auxiliary Space: O(1)

Insert an Element Near the Given Position

We can use the set::insert() function to insert the element near the given position. The std::set has to maintain the order of elements so we cannot force the insertion at any particular index.

Syntax

st.insert(pos, val)

Parameters

• val: Value which we have to insert.
• pos: Iterator specify the position nearby which the new element is to be inserted.

Return Value

• This version returns an iterator pointing to the newly inserted element or the already present copy of the element.

Example

// C++ Program to illustrate how to use // set::insert() to insert the value near // the specific position #include <bits/stdc++.h> using namespace std; int main() {  set<int> st = {34, 67, 12};    auto it = st.begin();  // Inserting an element 1 at  // starting position  st.insert(it, 1);  for (auto i : st)  cout << i << " ";  return 0; } 

1 12 34 67 

Time Complexity: O(log n)
Auxiliary Space: O(1)

Insert Multiple Elements

We can insert multiple elements in a set using set::insert() by enclosing the multiple value inside the braces {} and separate each of them using a comma. This form is called initializer list.

Syntax

st.insert({ val1,val2,....});

Parameters

• { val1,val2,....}: First value, second value and so on.

Return Value

• This version does not return anything.

Example

// C++ Program to illustrate, how to insert // multiple values using set::insert() #include <bits/stdc++.h> using namespace std; int main() {  set<int> st;  // Insting the multiple values  st.insert({12, 45, 11, 78, 9});    for (auto i : st)  cout << i << " ";  return 0; } 

9 11 12 45 78 

Time Complexity: O(k log n), where n is the number of elements already present in the set.
Auxiliary Space: O(k), where k is the number of elements to be inserted.

Insert Multiple Elements from a Range

The set::insert() function can also be used to insert multiple elements from the given range. This range can by any STL container.

Syntax

st.insert(first, last);

Parameters

• first: Iterator pointing to the starting position of the range.
• end: Iterator pointing to the position just after the last element of the range.

Return Value

• The version of the function does not return anything.

Example

// C++ program to illustrate how to use // set::insert to insert multiple element from // the given range of STL container #include <bits/stdc++.h> using namespace std; int main() {  vector<int> vec = {12, 45, 11, 67, 9};  // Define the range as whole vector  auto first = vec.begin();  auto last = vec.end();  // Insert elements of defined range  set<int> st(first, last);  for (auto i : st)  cout << i << " ";  return 0; } 

9 11 12 45 67 

Time Complexity: O(k log n), where n is the number of elements in the set.
Auxiliary Space: O(k), where k is the number of elements in the range.