What is an Unordered-multiset?

An unordered_multiset in STL is an associative container just like an unordered set the only difference is it can store duplicate elements in it.

Syntax:

unordered_multiset<object_type> variable_name;

Example:

unordered_multiset<int> s;
unordered_multiset<string> str;

Functions in multiset:

• insert() – to insert an element in the unordered multiset.

unordered_multiset<int> s;
s.insert(1);
s.insert(2);

• begin() – return an iterator pointing to the first element in the unordered multiset.

s.begin();

• end() – returns an iterator to the theoretical element after the last element.

s.end();

• count() – gives the count of a particular element in the unordered multiset.

unordered_multiset<int> s;
s.insert(1);
s.insert(2);
s.count(2); //returns 1

• clear() – deletes all the elements in the unordered multiset.

s.clear();

• find() – to search an element in the unordered multiset.

unordered_multiset<int> s;
s.insert(1);
s.insert(2);
if(s.find(2)!=s.end())
cout<<"true"<<endl;

• erase() – to delete a single element or elements between a particular range.

s.erase();

• size() – returns the size of the unordered multiset.

s.size();

• empty() – to check if the unordered multiset is empty or not.

s.empty();

Code:

#include<bits/stdc++.h>

using namespace std;

int main() {
  unordered_multiset < int > s;
  for (int i = 1; i <= 10; i++) {
    s.insert(i);
  }
  s.insert(5);
  cout << "Elements present in the unordered multiset: ";
  for (auto it = s.begin(); it != s.end(); it++) {
    cout << * it << " ";
  }
  cout << endl;
  int n = 2;
  if (s.find(2) != s.end())
    cout << n << " is present in unorderd multiset" << endl;

  s.erase(s.begin());
  cout << "Elements after deleting the first element: ";
  for (auto it = s.begin(); it != s.end(); it++) {
    cout << * it << " ";
  }
  cout << endl;

  cout << "The size of the unordered multiset is: " << s.size() << endl;

  if (s.empty() == false)
    cout << "The unordered multiset is not empty " << endl;
  else
    cout << "The unordered multiset is empty" << endl;
  s.clear();
  cout<<"Size of the unordered multiset after clearing all the elements: "<<s.size();
}

• cbegin() – it refers to the first element of the unordered multiset.
• cend() – it refers to the theoretical element after the last element of the unordered multiset.
• rbegin() – it points to the last element of the unordered multiset.
• rend() – it points to the theoretical element before the first element of the unordered multiset.
• emplace() – to insert an element in the unordered multiset.
• max_size() – the maximum elements an unordered multiset can hold.

Special thanks to Subhrajit Das for contributing to this article on takeUforward. If you also wish to share your knowledge with the takeUforward fam, please check out this article