std::unordered_multiset<Key,Hash,KeyEqual,Allocator>::size
Min standard notice:
Returns the number of elements in the container, i.e. std::distance(begin(), end()).
# Declarations
size_type size() const noexcept;
(since C++11)
# Return value
The number of elements in the container.
# Example
#include <cassert>
#include <unordered_set>
int main()
{
std::unordered_multiset<int> nums{4, 2, 4, 2};
assert(nums.size() == 4);
}