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unordered_map count() in C++

  • Difficulty Level : Easy
  • Last Updated : 26 Sep, 2018

The unordered_map::count() is a builtin method in C++ which is used to count the number of elements present in an unordered_map with a given key.

Note: As unordered_map does not allow to store elements with duplicate keys, so the count() function basically checks if there exists an element in the unordered_map with a given key or not.

Syntax:

size_type count(Key);

Parameters: This function accepts a single parameter key which is needed to be checked in the given unordered_map container.

Return Value: This function returns 1 if there exists a value in the map with the given key, otherwise it returns 0.



Below programs illustrate the unordered_map::count() function:

Program 1:




// C++ program to illustrate the 
// unordered_map::count() function
  
#include<iostream>
#include<unordered_map>
  
using namespace std;
  
int main()
{
    // unordered map
    unordered_map<int , string> umap;
      
    // Inserting elements into the map
    umap.insert(make_pair(1,"Welcome"));
    umap.insert(make_pair(2,"to"));
    umap.insert(make_pair(3,"GeeksforGeeks"));
      
    // Check if element with key 1 is present using 
    // count() function
    if(umap.count(1))
    {
        cout<<"Element Found"<<endl;
    }
    else
    {
        cout<<"Element Not Found"<<endl;    
    }
      
    return 0;
}
Output:
Element Found

Program 2:




// C++ program to illustrate the 
// unordered_map::count() function
  
#include<iostream>
#include<unordered_map>
  
using namespace std;
  
int main()
{
    // unordered map
    unordered_map<int , string> umap;
      
    // Inserting elements into the map
    umap.insert(make_pair(1,"Welcome"));
    umap.insert(make_pair(2,"to"));
    umap.insert(make_pair(3,"GeeksforGeeks"));
      
    // Try inserting element with
    // duplicate keys
    umap.insert(make_pair(3,"CS Portal"));
      
    // Print the count of values with key 3
    // to check if duplicate values are stored 
    // or not
    cout<<"Count of elements in map, mapped with key 3: "
            <<umap.count(3);
      
    return 0;
}
Output:
Count of elements in map, mapped with key 3: 1
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