unordered_multiset erase() function in C++ STL

Last Updated : 29 Aug, 2024

The unordered_multiset::erase() function is a built-in function in C++ STL which is used to remove either a single element or, all elements with a definite value or, a range of elements ranging from start(inclusive) to end(exclusive). This decreases the size of the container by the number of elements removed.

Syntax

unordered_multiset_name.erase(iterator position)
unordered_multiset_name.erase(iterator start, iterator end)
unordered_multiset_name.erase(key_value)

Parameters

This function has three versions.

The first one takes an iterator as an argument, erases the element present at that position.
The second version takes two iterator(say start and end) takes 2 iterators as argument and erases all elements in the range [start, end).
The third version takes a key value as argument and erases all elements of that value in the multiset.

Return Value

The 1st and 2nd version of the function as shown in the above syntax returns an iterator immediately following the last element erased. The 3rd version returns the number of element erased. Below programs illustrate the unordered_multiset::erase() function:

Program 1

CPP

// C++ program to illustrate the // unordered_multiset::erase() function #include <iostream> #include <unordered_set> using namespace std; int main(){  unordered_multiset<int> samplemultiSet;  // Inserting elements  samplemultiSet.insert(10);  samplemultiSet.insert(5);  samplemultiSet.insert(15);  samplemultiSet.insert(20);  samplemultiSet.insert(25);  samplemultiSet.insert(10);  samplemultiSet.insert(15);  samplemultiSet.insert(20);  // Erases a particular element by its position  samplemultiSet.erase(samplemultiSet.begin());  // Displaying the set after removal  for (auto it = samplemultiSet.begin();   it != samplemultiSet.end(); it++) {  cout << *it << " ";  }  // erases a range of elements,   // here all the elements  samplemultiSet.erase(samplemultiSet.begin(),   samplemultiSet.end());  cout << "\nMultiSet size: " << samplemultiSet.size();  return 0; }

Output

20 20 15 15 5 10 10 MultiSet size: 0

Time Complexity: O(n), where n is the number of occurrences of the value 10.
Auxiliary Space: O(1)

Program 2

CPP

// C++ program to illustrate the // unordered_multiset::erase() function #include <iostream> #include <unordered_set> using namespace std; int main(){  unordered_multiset<int> samplemultiSet;  // Inserting elements  samplemultiSet.insert(10);  samplemultiSet.insert(5);  samplemultiSet.insert(15);  samplemultiSet.insert(20);  samplemultiSet.insert(25);  samplemultiSet.insert(10);  samplemultiSet.insert(15);  samplemultiSet.insert(20);  // Erases all elements of value 10  samplemultiSet.erase(10);  // Displaying the set after removal  for (auto it = samplemultiSet.begin();   it != samplemultiSet.end(); it++) {  cout << *it << " ";  }  return 0; }