std::count() in C++ STL
Last Updated :
26 Feb, 2023
std::count() returns the number of occurrences of an element in a given range. Returns the number of elements in the range [first, last) that compare equal to val.
If the val is not found at any occurrence then it returns 0(Integer value).
// Returns count of occurrences of value in // range [begin, end] int count(Iterator first, Iterator last, T &val) first, last : Input iterators to the initial and final positions of the sequence of elements. val : Value to match
Complexity It’s order of complexity O(n). Compares once each element with a particular value. Counting occurrences in an array.
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 3, 2, 1, 3, 3, 5, 3 };
int n = sizeof (arr) / sizeof (arr[0]);
cout <<
" Number of times 3 appears : "
<< count(arr, arr + n, 3);
return 0;
}
|
Output
Number of times 3 appears : 4
Time complexity: O(n)
Here n is size of array.
Auxiliary Space: O(1)
As constant extra space is used.
Counting occurrences in a vector.
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
vector< int > vect{ 3, 2, 1, 3, 3, 5, 3 };
cout << "Number of times 3 appears : "
<< count(vect.begin(), vect.end(), 3);
return 0;
}
|
Output
Number of times 3 appears : 4
Time complexity: O(n)
Here n is size of vector.
Auxiliary Space: O(1)
As constant extra space is used.
Counting occurrences in a string.
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
string str = "geeksforgeeks" ;
cout << "Number of times 'e' appears : "
<< count(str.begin(), str.end(), 'e' );
return 0;
}
|
Output
Number of times 'e' appears : 4
Time complexity: O(n)
Here n is the length of string.
Auxiliary Space: O(1)
As constant extra space is used.
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