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.
// C++ program for count in C++ STL for // array #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;
} |
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.
// C++ program for count in C++ STL for // a vector #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;
} |
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.
// C++ program for the count in C++ STL // for a string #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;
} |
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.