unordered_set equal_range in C++ STL

equal_range() in general returns range that includes all elements equal to given value. For unordered_set where all keys are distinct, the returned range contains at-most one element. 

Syntax

 setname.equal_range(key name)

Arguments It takes the key to be searched as parameter. 

Return Value It returns two iteraters—- lower and upper bound of the range that contains the key. 

Example

CPP

// C++ program to illustrate the
// unordered_set::equal_range function
#include <iostream>
#include <unordered_set>
using namespace std;
int main()
{
    // declaration
    unordered_set<int> sample;

    // Insert some values
    sample.insert({ 20, 30, 40 });

    // Test the equal_range function for
    // a given key if it does exists
    auto range1 = sample.equal_range(20);
    if (range1.first != sample.end()) {
        for (; range1.first != range1.second; ++range1.first)
            cout << *range1.first << endl;
    }
    else
        cout << "Element does not exist";
    return 0;
}

Output

20

CPP

// C++ program to illustrate the
// unordered_set::equal_range function
#include <iostream>
#include <unordered_set>
using namespace std;
int main()
{

    // declaration
    unordered_set<int> sample;

    // Insert some values
    sample.insert({ 20, 30, 40 });

    // Test the equal_range function
    // for a given key if it does not exist
    auto range1 = sample.equal_range(60);
    if (range1.first != sample.end()) {
        for (; range1.first != range1.second; ++range1.first)
            cout << *range1.first << endl;
    }
    else
        cout << "Element does not exist";
    return 0;
}

Output

Element does not exist

Time complexity: O(n)