Vowels of All Substrings — LeetCode 2063 Python Solution

The problem

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.

Example

Input

word = "aba"

Output

6

Explanation

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

Python solution

class Solution:
    def countVowels(self, word: str) -> int:
        n = len(word)
        return sum((i + 1) * (n - i) for i, c in enumerate(word) if c in 'aeiou')

Complexity

Pattern: Dynamic Programming

Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 2063. Vowels of All Substrings is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Dynamic Programming.

The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.

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