We recently saw a tutorial on Vectors in C++. Now its time for better things. So we all know what a set is. It is a group of elements in which there is no duplicate.

Consider we need a container with following features:

-> add an element, but do not allow duplicates

-> remove elements

-> get count of elements (distinct elements)

-> check whether elements are present in set

The container we have to use here is a "set". Set can add, remove and check the presence of particular element in O(log N), where N is the count of objects in the set.

Since set is not a linear container, it’s impossible to take the element in set by index. Thus, we traverse the elements of set using iterators.

To determine whether some element is present in set use 'find()' member function. There are several 'find()' ’s in STL. There is a global algorithm 'find()', which takes two iterators, element, and works for O(N). While searching in set and map do not use global find – instead, use member function 'set::find()'. As 'ordinal' find, set::find will return an iterator, either to the element found, or to 'end()'. So, the element presence check looks like this:

To erase an element from set use the erase() function.

The erase() function also has the interval form:

Set has an interval constructor as well:

It gives us a simple way to get rid of duplicates in vector, and sort it:

Last but not the least, here 'h1' will contain the same elements as 'h' but

I hope now you realize the power of STL library in C++

Consider we need a container with following features:

-> add an element, but do not allow duplicates

-> remove elements

-> get count of elements (distinct elements)

-> check whether elements are present in set

The container we have to use here is a "set". Set can add, remove and check the presence of particular element in O(log N), where N is the count of objects in the set.

Code:

set<int> r; for(int i = 1; i <= 50; i++) { r.insert(i); // Insert 50 elements, [1..50] } s.insert(4); // does nothing, 4 already exists in set for(int i = 2; i <= 50; i += 2) { s.erase(i); // Erase even values } int n = int(s.size()); // n will be 25

Code:

// Calculate the sum of elements in set set<int> S; // ... int r = 0; for(set<int>::const_iterator it = S.begin(); it != S.end(); it++) { r += *it; }

Code:

set<int> s; // ... if(s.find(4) != s.end()) { // 4 present in set } else { // 4 not present in set }

Code:

set<int> s; // … s.insert(54); s.erase(29);

Code:

set<int> s; // .. set<int>::iterator it1, it2; it1 = s.find(10); it2 = s.find(100); // Will work if it1 and it2 are valid iterators, i.e. values 10 and 100 present in set. s.erase(it1, it2); // Note that 10 will be deleted, but 100 will remain in the container

Code:

int d[5] = { 7, 8, 4, 2, 6 }; set<int> S(d, d+5);

Code:

vector<int> h; // … set<int> r(all(h)); vector<int> h1(all(r));

**sorted in ascending order**and with**duplicates removed.**I hope now you realize the power of STL library in C++