What is the NavigableSet.headSet() method in Java?

The `unordered_map::count()` function is available in the `<unordered_map>` header file in `C++`. 

The **`unordered_map::count()`** is used to count the number of elements in an unordered map with the specified key. The Unordered map does not allow repetition that’s why this method will return the count to be either $1$ or $0$.


#    
#  Syntax
The syntax of the `unordered_map::count()` function is given below:
```
boolean count(K key);
```

#    
## Function parameter(s)
The `unordered_map::count()` method accepts the parameters mentioned below: 
* **Key:** The key whose count needs to be returned in the unordered map.


##    
## Return
The `unordered_map::count()` returns one of the two values:
* **True (1):** If the specified key element is present in the unordered map, the function returns a value of $1$ which can also be treated as a boolean `true`. It return $1$ because the unordered map does not allow repetition of elements.
* **False (0):** If the specified key element is not present in the unordered map, the function returns a value of $0$ which can also be treated as a boolean `false`. It return $0$ because the unordered map does not allow repetition of elements.

# Code
Let us have a look at the code now.


#include <iostream>
#include <unordered_map>
using namespace std;

int main()
{
  // Initialising unordered map 
  unordered_map<int,string> umap ={
                            {12, "unordered"},
                            {16, "map"},
                            {89, "in"},
                            {66, "C++"}
                          };

  // Using unordered_map::count() function   
  if(umap.count(66)) 
    cout<<"The element with specified key is present."<<endl;
  else
    cout<<"The element with specified key is absent."<<endl;

  return 0;
}

## Explanation of the code above

* In lines # 1 and 2, we imported the required header files.
* In line # 5, we made a `main()` function.
* From lines # 8-13, we initialized an unordered map with integer type keys and string type values. 
* In lines 16-19, we used `unordered_map::count()` function to check the presence of the element with the specified key and displayed the message accordingly.


In this way, you can quickly check whether the element is already present in the map or not using the `count()` function.

What is the unordered_map::count() function in C++?

This function counts elements with a specified key in an unordered map, returning either 1 (key present) or 0 (key absent).