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Level up your coding skills with
the C++ Standard Template
Library (STL):
Sets
BY JOYJIT CHOUDHURY
Unordered Set
The unordered_set is a container that stores unique
elements in no particular order. It allows fast retrieval of
individual elements based on their value.
It is typically implemented as a hash table, where the
value of the element is also it’s key
Search, insertion, and removal have an average time
complexity of O(1)
Defined in the header <unordered_set>
Belongs to the namespace std
(remember : using namespace std)
Insertion of elements
uSet
uSet.insert(12);
uSet
12
uSet
12
uSet.insert(24);
24
Insertion of elements
uSet
12
uSet.insert(24);
24
uSet
12 24
uSet
12 24
uSet.insert(12);
uSet.insert(36);
uSet
12 24
36
Remove elements
uSet.erase(24);
uSet
12 24
36
uSet
12
36
Remove elements
uSet
12
uSet
12
uSet
12
uSet.erase(36);
Search for an element
Member function find(), searches the container for an
element with a particular value. If such an element exists, it
returns an iterator to that element. Otherwise it returns an
iterator to unordered_set::end (the element past the end of
the container)
Another function count(), can be used to check whether
an element exists or not. It returns 1, if the desired element
exists, otherwise it returns 0
Number of elements
Member function size(), returns the number of elements in the unordered set
Is it empty?
Member function empty(), returns true if the unordered set is empty, falseotherwise
Set
The set is a container that stores unique elements in a particular
order. Sorting is done using the comparison function compare
It is typically implemented as a balanced binary search tree, where
the value of the element is also it’s key
Search, insertion, and removal have an average time complexity of
O(logN)
Defined in the header <set>
Belongs to the namespace std
(remember : using namespace std)
Set Search, insertion, and removal of elements with respect to set can
be done in the same way as that for unordered_set using the
functions insert(), erase(), find().
The difference being, the different time complexities of these
operations with respect to the different containers
O(1) : unordered_set vs. O(logN) : set
Member functions size(), empty() also perform the same actions for
set as they do for unordered_set
The elements in set are stored in a particular order and allow range
based iterations, whereas unordered_set stores the elements in a
random order
That’s not all. There are many other functions
and techniques that could come in handy.
Read about them on cplusplus.com or
cppreference.com or somewhere else. Just
google it !
