unordered_set count() function in C++ STL

The unordered_set::count() function is a built-in function in C++ STL which is used to count occurrences of a particular element in an unordered_set container. As the unordered_set container does not allows to store duplicate elements so this function is generally used to check if an element is present in the container or not. The function returns 1 if the element is present in the container otherwise it returns 0.

Syntax:

unordered_set_name.count(element)

Parameter: This function accepts a single parameter element. This parameter represents the element which is needed to be checked if it is present in the container or not.

Return Value: This function returns 1 if the element is present in the container otherwise it returns 0.

Below programs illustrate the unordered_set::count() function:

Program 1:

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// CPP program to illustrate the
// unordered_set::count() function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
  
    unordered_set<int> sampleSet;
  
    // Inserting elements
    sampleSet.insert(5);
    sampleSet.insert(10);
    sampleSet.insert(15);
    sampleSet.insert(20);
    sampleSet.insert(25);
  
    // displaying all elements of sampleSet
    cout << "sampleSet contains: ";
    for (auto itr = sampleSet.begin(); itr != sampleSet.end(); itr++) {
        cout << *itr << " ";
    }
  
    // checking if element 20 is present in the set
    if (sampleSet.count(20) == 1) {
        cout << "\nElement 20 is present in the set";
    }
    else {
        cout << "\nElement 20 is not present in the set";
    }
  
    return 0;
}

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Output:

sampleSet contains: 25 5 10 15 20 
Element 20 is present in the set

Program 2:

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// C++ program to illustrate the
// unordered_set::count() function
  
#include <iostream>
#include <unordered_set>
  
using namespace std;
  
int main()
{
  
    unordered_set<string> sampleSet;
  
    // Inserting elements
    sampleSet.insert("Welcome");
    sampleSet.insert("To");
    sampleSet.insert("GeeksforGeeks");
    sampleSet.insert("Computer Science Portal");
    sampleSet.insert("For Geeks");
  
    // displaying all elements of sampleSet
    cout << "sampleSet contains: ";
    for (auto itr = sampleSet.begin(); itr != sampleSet.end(); itr++) {
        cout << *itr << " ";
    }
  
    // checking if element GeeksforGeeks is
    // present in the set
    if (sampleSet.count("GeeksforGeeks") == 1) {
        cout << "\nGeeksforGeeks is present in the set";
    }
    else {
        cout << "\nGeeksforGeeks is not present in the set";
    }
  
    return 0;
}

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Output:

sampleSet contains: Welcome To GeeksforGeeks For Geeks Computer Science Portal 
GeeksforGeeks is present in the set


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