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C++ Unordered Set Find

The C++ std::unordered_set::find() function is used to find or search an element with key equivalent to key k in the container and returns an iterator if it is found, otherwise it returns an iterator to unordered_set::end().

The unordered_set is an associative container that contains a set of unique objects of type key. Every operation like insertion, search, and removal in an unordered_set has constant-time complexity.

Following is the syntax for std::unordered_set::find() function.

iterator find ( const key_type& k );
const_iterator find ( const key_type& k ) const;

• k − It indicates the key to be searched for.

It returns an iterator to the element if the specified value is found; otherwise, it returns unordered_set::end if it is not found in the container.

Let's look at the following example, where we are going to demonstrate the usage of unordered_set::find() function.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<string> myset = { "sai","ram","krishna" };
   //searching a key "ram"
   unordered_set<string>::const_iterator got = myset.find ("ram");
   if ( got == myset.end() )
      cout << "not found in myset";
   else
      cout << *got << " is in myset";
   cout << endl;
   return 0;
}

If we run the above code it will generate the following output −

ram is in myset

Consider the following example, where we are going to check whether the specified key is available or not.

#include <iostream>
#include <string>
#include <unordered_set>
using namespace std;

int main () {
   unordered_set<int> myset = { 10, 100, 1000, 10000 };
   
   if ( myset.find(100) != myset.end() )
      cout<< "100 is available in unordered set! "<<endl;
   if ( myset.find(1000) != myset.end() )
      cout<< "1000 is available in unordered set! "<<endl;
   else
      cout<< "specified key is not available in unordered set! "<<endl;
      
   return 0;
}

Following is the output of the above code −

100 is available in unordered set! 
1000 is available in unordered set! 

In the following example, we are going to erase the element that is found and display the left over elements.

#include <iostream>
#include <unordered_set>
using namespace std;
 
int main (){
   unordered_set<int> myUset{50, 500, 10, 100, 200};
   unordered_set<int>::iterator it;

   it = myUset.find(50);
   myUset.erase(it);
   myUset.erase(myUset.find(10));

   cout<<"myUset contains: ";
   for(it = myUset.begin(); it != myUset.end(); ++it)
      cout<<*it<<" ";

   return 0;
}

Output of the above code is as follows −

myUset contains: 200 100 500 

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