HASHSET IN C++

An unordered collection that consists of unique elements is called a hashset in c++. The standard operation collection, like remove, contains is contained in c++. Intersection, symmetric difference, and union are the standard set-based operation constituted by c++. For identification and searching of items, the hash function in hashset is very useful in c++. The hashset takes an important role in the identification of duplicates in the consisting list. By this hash function, we can get the distinct values and even the duplicate values as well. The unordered_ list (hashset) takes some time that is o ( 1 ) which is constant in nature. In the other case, the taken time can be o (n) which is linear time. In this context, we would learn all about the hashset in c++.

Syntax:

The syntax for the insertion of hashset or unordered set in c++, which is a string type, is as follows:

int main()
{
unordered_set <string> CBA ;
CBA.insert("") ;
CBA.insert("") ;
..................
}

Some examples of C++ hashset with their working mechanism:

An unordered_set or HashSet is a set in which the key is stored in any order. For a HashSet, there are many functions used. But the most commonly used functions are stated below:

The size function is used for capacity.
empty function is also used for capacity.
find is used to search for a key.
Erase function is used for modification in it.
The insert function is also used for modification.

An unordered_set allows only the unique keys, and an unordered_multiset allows only the duplicate keys through it.

Examples:

With the different types of examples, the whole working mechanism of C++ HashSet has been explained as follows:

1) c++ hashset example using {…...} That is an initialized list:

Using HashSet in C++, the basic example is given in which we have initialized the set with the help of initializer list {…..}.

Code:

#include <iostream>
#include <unordered_set>
int main()
{
std::unordered_set<int> P { 2017, 2016, 2015 };
for (auto Q: P)
std::cout << Q << '\n';
return 0;
}

Output:

2015
2016
2017

2) Use of binary predicate for the passing of comparison object:

Using a binary predicate set, the comparison objects are passed in the given an example below. The set ordering is defined using two same types of elements.

Code:

#include <iostream>
#include <set>
struct JAVATPOINT {
template<typename X>
bool operator()(const X& n, const X& p) const
{
return n > p;
}
};
int main()
{
std::set<int, JAVATPOINT> values = { 120, 80, 250 };
for (auto S: values)
std::cout << S << '\n';
return 0;
}

Output:

250
120
80

3) Example of hashset in C++ using insert, iteration, find, and declaration:

In the example given below, constant time is taken on average for the insert, erase and find operation. The find function is given in the example when in the set, the key is not present. It returns the Iterator to the end(). And the other hand, the Iterator easily comes back to the key position when in the set, the key is present. For the key values as a pointer, Iterator is used for receiving the key, And the key can be retrieved using dereferencing * operator.

Code:

#include <bits/stdc++.h>
using namespace std;
int main()
{
unordered_set <string> CBA ;
CBA.insert("Developer") ;
CBA.insert("Programmer") ;
CBA.insert("tester") ;
CBA.insert("HR") ;
CBA.insert("Coder") ;
string key = "JAVATPOINT" ;
if (CBA.find(key) == CBA.end())
cout << key << " one of the best company." << endl << endl ;
else
cout << "retrieved" << key << endl << endl ;
key = "Programmer";
if (CBA.find(key) == CBA.end())
cout << key << "can not retrieve\n" ;
else
cout << "retrieved " << key << endl ;
cout << "\nhere is the designations : " <<endl;
unordered_set<string> :: iterator itr;
for (itr = CBA.begin(); itr != CBA.end(); itr++)
cout << (*itr) << endl;
}

Output:

JAVATPOINT one of the best company.

retrieved Programmer

here is the designations :
HR
tester
Programmer
Coder
Developer

When the key data is not found in the order list:
JAVATPOINT one of the best company

Program can not retrieve

here is the designations :
HR
tester
Programmer
Coder
Developer

4) Using an unordered set searching for duplicate content:

In the given below example as the input, the set of integers is provided, and in the set, the duplicates have been found and displayed in the output.

Code example:

#include <bits/stdc++.h>
using namespace std;
void printDuplicates(int deepak[], int M)
{
unordered_set<int> JAVATPOINT;
unordered_set<int> similar;

for (int P = 0; P < M; P++)
{
if (JAVATPOINT.find(deepak[P]) == JAVATPOINT.end())
JAVATPOINT.insert(deepak[P]);
else
similar.insert(deepak[P]);
}
cout << "similar contents are : ";
unordered_set<int> :: iterator start;
for (start = similar.begin(); start != similar.end(); start++)
cout << *start << " ";
}
int main()
{
int deepak[] = {9, 3, 6, 1, 6, 2, 4, 9, 5, 7, 0, 8};
int M = sizeof(Deepak) / sizeof(int);
printDuplicates(Deepak, M);
return 0;
}

Output:

similar contents are : 9 6

Conclusion:

In the above context, we have learned about HashSet in C++ and its working mechanism of it. In this article, we have also learned the various applications of C++ has set with the help of different examples in which they are working. In finding duplicate content and desired content C++ HashSet plays a vital role in it.

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