# unordered_multimap count() function in C++ STL

• Last Updated : 28 Dec, 2022

The unordered_multimap::count() is a built-in function in C++ STL that returns the number of elements in the container whose key is equal to the key passed in the parameter. Syntax:

`unordered_multimap_name.count(key)`

Parameters: The function accepts a single mandatory parameter key that specifies the key whose count in the unordered_multimap container is to be returned. Return Value: It returns an unsigned integral type which denotes the number of times a key occurs in the container.

Time Complexity: O(N)

Below programs illustrates the above function: Program 1:

## CPP

 `// C++ program to illustrate the``// unordered_multimap::count()``#include ``using` `namespace` `std;` `int` `main()``{` `    ``// declaration``    ``unordered_multimap<``int``, ``int``> sample;` `    ``// inserts key and element``    ``sample.insert({ 10, 100 });``    ``sample.insert({ 10, 100 });``    ``sample.insert({ 20, 200 });``    ``sample.insert({ 30, 300 });``    ``sample.insert({ 30, 150 });` `    ``cout << ``"10 occurs "` `<< sample.count(10)``        ``<< ``" times"``;` `    ``cout << ``"\n20 occurs "` `<< sample.count(20)``        ``<< ``" times"``;` `    ``cout << ``"\n13 occurs "` `<< sample.count(13)``        ``<< ``" times"``;` `    ``cout << ``"\n30 occurs "` `<< sample.count(30)``        ``<< ``" times"``;` `    ``return` `0;``}`

Output:

```10 occurs 2 times
20 occurs 1 times
13 occurs 0 times
30 occurs 2 times```

Program 2:

## CPP

 `// C++ program to illustrate the``// unordered_multimap::count()``#include ``using` `namespace` `std;` `int` `main()``{` `    ``// declaration``    ``unordered_multimap<``char``, ``char``> sample;` `    ``// inserts key and element``    ``sample.insert({ ``'a'``, ``'b'` `});``    ``sample.insert({ ``'a'``, ``'b'` `});``    ``sample.insert({ ``'b'``, ``'c'` `});``    ``sample.insert({ ``'r'``, ``'a'` `});``    ``sample.insert({ ``'r'``, ``'b'` `});` `    ``cout << ``"a occurs "` `<< sample.count(``'a'``)``        ``<< ``" times"``;` `    ``cout << ``"\nb occurs "` `<< sample.count(``'b'``)``        ``<< ``" times"``;` `    ``cout << ``"\nz occurs "` `<< sample.count(``'z'``)``        ``<< ``" times"``;` `    ``cout << ``"\nr occurs "` `<< sample.count(``'r'``)``        ``<< ``" times"``;` `    ``return` `0;``}`

Output:

```a occurs 2 times
b occurs 1 times
z occurs 0 times
r occurs 2 times```

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