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:
1 <= word.length <= 105wordconsists of lowercase English letters.
[Math] [String] [Dynamic Programming] [Combinatorics]
