unordered_set bucket() function in C++ STL

The unordered_set::bucket() method is a builtin function in C++ STL which returns the bucket number of a specific element. That is, this function returns the bucket number where a specific element is stored in the unordered_set container. The bucket is a slot in the unordered_set’s internal hash table where elements are stored. 

Note: Buckets in unordered_set are numbered from 0 to n-1, where n is the total number of buckets. 

Syntax:

unordered_set_name.bucket(element);

Parameter: This is a mandatory parameter and specifies the value of the element whose bucket number is needed to know in the unordered_set container. 

Return Value: This function returns the bucket number of the bucket in the unordered_set container where the element with value element is stored. 

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

CPP

// C++ program to illustrate the
// unordered_set::bucket() 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);

    for (auto itr = sampleSet.begin(); itr != sampleSet.end(); itr++) {
        cout << "The Element " << (*itr) << " is present in the bucket: "
            << sampleSet.bucket(*itr);
        cout << endl;
    }

    return 0;
}

Output:

The Element 25 is present in the bucket: 3
The Element 5 is present in the bucket: 5
The Element 10 is present in the bucket: 10
The Element 15 is present in the bucket: 4
The Element 20 is present in the bucket: 9

Time complexity: O(1)