unordered_multimap count() function in C++ STL (original) (raw)

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:

u_norderedmultimapname_.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 <bits/stdc++.h> 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 <bits/stdc++.h> 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