c++ O(N) solution 5 lines 
Intuitiontry to cnt all substring including the charcterApproachcounting the substringComplexity
Time complexity: O(N)

Space complexity:O(1)
Code
# Intuition
<!-- Describe your first thoughts on how to solve this problem. -->
try to cnt all substring including the charcter 
# Approach
<!-- Describe your approach to solving the problem. -->
counting the substring 
# Complexity
- Time complexity: O(N)
<!-- Add your time complexity here, e.g. $$O(n)$$ -->

- Space complexity:O(1)
<!-- Add your space complexity here, e.g. $$O(n)$$ -->

# Code
```cpp []
class Solution {
public:

    

    long long countVowels(string word) {
        int n = word.length() ;
        long long cnt = 0 ;
        for ( int i = 0 ; i < word.length() ; i++ ){
            if ( word[i] == 'a' || word[i] == 'u' || word[i] == 'i' || word[i] == 'e' || word[i] == 'o' ){
                cnt += ((long long) i + 1 ) * ( n - i ) ;
            }
        }
        return cnt ;
    }
};
```
['C++']