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C++ Sets
In C++, a Set is a part of the Standard Template Library (STL) that stores unique elements in a specific order. Sets automatically sort their elements and remove duplicates, making them ideal for tasks where uniqueness is important, such as maintaining a list of distinct values or removing duplicates from a dataset.
Sets use a balanced binary search tree (usually a Red-Black Tree) internally, which ensures that operations like insertion, deletion, and search all happen in logarithmic time complexity O(log n).
Key Features of Sets in C++
-
All elements in a set are unique; duplicates are automatically removed.
-
Elements are stored in sorted order by default.
-
Once an element is inserted, its value cannot be modified, though it can be removed and reinserted.
-
Sets provide efficient search, insertion, and deletion operations.
-
Sets are part of the
<set>header file in C++ STL.
Syntax of C++ Set
To use a set, include the header <set> and declare it using the following syntax:
#include <iostream>
#include <set>
using namespace std;
int main() {
set<int> numbers;
numbers.insert(10);
numbers.insert(20);
numbers.insert(10); // duplicate, ignored
for (int num : numbers) {
cout << num << " ";
}
return 0;
}
Output:
10 20
In this example, the duplicate value 10 is automatically ignored. The set keeps elements in ascending order.
Types of Sets in C++
C++ provides two main types of sets:
-
set – stores elements in ascending order by default.
-
multiset – allows duplicate elements and also keeps them sorted.
Example of a multiset:
#include <iostream>
#include <set>
using namespace std;
int main() {
multiset<int> nums = {10, 20, 10, 30};
for (int n : nums) {
cout << n << " ";
}
return 0;
}
Output:
10 10 20 30
Important Member Functions of Set
Here are some commonly used functions in C++ sets:
| Function | Description |
|---|---|
insert(value) |
Adds an element to the set |
erase(value) |
Removes an element from the set |
find(value) |
Returns iterator to the value if found |
count(value) |
Returns 1 if element exists, otherwise 0 |
clear() |
Removes all elements from the set |
size() |
Returns the number of elements |
empty() |
Checks if the set is empty |
begin() / end() |
Returns iterator to start and end of the set |
Example: Basic Set Operations
#include <iostream>
#include <set>
using namespace std;
int main() {
set<int> nums = {5, 2, 8, 1};
cout << "Set elements: ";
for (int x : nums)
cout << x << " ";
nums.insert(3);
nums.erase(8);
cout << "\nAfter modifications: ";
for (int x : nums)
cout << x << " ";
return 0;
}
Output:
Set elements: 1 2 5 8
After modifications: 1 2 3 5
Example: Searching in a Set
#include <iostream>
#include <set>
using namespace std;
int main() {
set<string> names = {"Anita", "Pooja", "Kavya"};
string searchName = "Pooja";
if (names.find(searchName) != names.end())
cout << searchName << " found in set.";
else
cout << searchName << " not found.";
return 0;
}
Output:
Pooja found in set.
Example: Using count() in Set
#include <iostream>
#include <set>
using namespace std;
int main() {
set<int> nums = {1, 2, 3, 4};
cout << "Is 3 present? " << nums.count(3) << endl;
cout << "Is 9 present? " << nums.count(9) << endl;
return 0;
}
Output:
Is 3 present? 1
Is 9 present? 0
Iterating Over a Set
You can iterate over a set using iterators as well:
for (set<int>::iterator it = nums.begin(); it != nums.end(); ++it) {
cout << *it << " ";
}
This method gives you more control if you want to erase elements during iteration or access them conditionally.
Erasing Elements from a Set
You can remove elements from a set in three ways:
-
By value –
set.erase(value) -
By position –
set.erase(iterator) -
By range –
set.erase(start_iterator, end_iterator)
Example:
nums.erase(2); // Removes element 2
nums.erase(nums.begin()); // Removes first element
nums.erase(nums.begin(), nums.find(5)); // Removes range
Example: Set of Strings
#include <iostream>
#include <set>
using namespace std;
int main() {
set<string> fruits = {"Apple", "Banana", "Mango", "Apple"};
for (auto f : fruits)
cout << f << " ";
return 0;
}
Output:
Apple Banana Mango
Summary of the Tutorial
C++ sets are an excellent choice for storing unique, sorted data efficiently. They automatically handle duplicate removal and keep elements organized in ascending order. Sets come with a variety of built-in operations like insertion, deletion, and searching, all performed in O(log n) time. When duplicates are allowed, you can use a multiset instead.
Sets are commonly used in real-world applications like filtering unique records, maintaining sorted datasets, and performing quick searches in large data collections.
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Launch Free Live Code EditorPractice Questions
-
Write a C++ program to create a set of integers and perform insert, erase, and display operations.
-
Create a program that takes a list of numbers from the user and removes duplicates using a set.
-
Write a C++ program to find whether a given element exists in a set using the
find()function. -
Build a program that counts how many unique characters are present in a string using a set.
-
Write a C++ program to merge two sets and display all unique elements in ascending order.
-
Create a program that finds the intersection of two sets.
-
Write a C++ program to store names in a set and display them in alphabetical order.
-
Build a program that removes all elements greater than a given number from a set.
-
Write a program to compare two sets and check whether they contain the same elements.
-
Create a C++ program to demonstrate the difference between a set and a multiset using integer values.
