Count vowel strings in ranges

Array String Prefix Sum

67.8% acceptance

Feb 25, 2026

1173

You are given a 0-indexed array of strings words and a 2D array of integers queries. Each query queries[i] = [li, ri] asks us to find the number of strings present at the indices ranging from li to ri (both inclusive) of words that start and end with a vowel. Return an array ans of size queries.length, where ans[i] is the answer to the ith query. Note that the vowel letters are 'a', 'e', 'i', 'o', and 'u'.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn vowel_strings(words: Vec<String>, queries: Vec<Vec<i32>>) -> Vec<i32> {
    let vowels = |c: char| matches!(c, 'a' | 'e' | 'i' | 'o' | 'u');
    let n = words.len();
    let mut prefix = vec![0i32; n + 1];
    for (i, w) in words.iter().enumerate() {
      let chars: Vec<char> = w.chars().collect();
      let ok = vowels(*chars.first().unwrap()) && vowels(*chars.last().unwrap());
      prefix[i + 1] = prefix[i] + if ok { 1 } else { 0 };
    }
    queries
      .iter()
      .map(|q| prefix[q[1] as usize + 1] - prefix[q[0] as usize])
      .collect()
  }
}