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unordered_multimap count() function in C++ STL

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  • Last Updated : 28 Dec, 2022
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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 <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

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