2063 - Vowels of All Substrings\.

Medium

Given a string word, return the sum of the number of vowels ('a', 'e', 'i', 'o', and 'u') in every substring of word.

A substring is a contiguous (non-empty) sequence of characters within a string.

Note: Due to the large constraints, the answer may not fit in a signed 32-bit integer. Please be careful during the calculations.

Example 1:

Input: word = "aba"

Output: 6

Explanation: All possible substrings are: "a", "ab", "aba", "b", "ba", and "a".

• "b" has 0 vowels in it

• "a", "ab", "ba", and "a" have 1 vowel each

• "aba" has 2 vowels in it

Hence, the total sum of vowels = 0 + 1 + 1 + 1 + 1 + 2 = 6.

Example 2:

Input: word = "abc"

Output: 3

Explanation: All possible substrings are: "a", "ab", "abc", "b", "bc", and "c".

• "a", "ab", and "abc" have 1 vowel each

• "b", "bc", and "c" have 0 vowels each

Hence, the total sum of vowels = 1 + 1 + 1 + 0 + 0 + 0 = 3.

Example 3:

Input: word = "ltcd"

Output: 0

Explanation: There are no vowels in any substring of "ltcd".

Constraints:

• <code>1 <= word.length <= 10⁵</code>

• word consists of lowercase English letters.