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Count the Number of Vowel Strings in Range

EasyUpdated: Aug 2, 2025
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LeetCode

Problem

You are given a 0-indexed array of string words and two integers left and right.

A string is called a vowel string if it starts with a vowel character and ends with a vowel character where vowel characters are 'a', 'e', 'i', 'o', and 'u'.

Return the number of vowel stringswords[i]wherei belongs to the inclusive range[left, right].

Examples

Example 1

Input: words = ["are","amy","u"], left = 0, right = 2
Output: 2
Explanation: 
- "are" is a vowel string because it starts with 'a' and ends with 'e'.
- "amy" is not a vowel string because it does not end with a vowel.
- "u" is a vowel string because it starts with 'u' and ends with 'u'.
The number of vowel strings in the mentioned range is 2.

Example 2

Input: words = ["hey","aeo","mu","ooo","artro"], left = 1, right = 4
Output: 3
Explanation: 
- "aeo" is a vowel string because it starts with 'a' and ends with 'o'.
- "mu" is not a vowel string because it does not start with a vowel.
- "ooo" is a vowel string because it starts with 'o' and ends with 'o'.
- "artro" is a vowel string because it starts with 'a' and ends with 'o'.
The number of vowel strings in the mentioned range is 3.

Constraints

  • 1 <= words.length <= 1000
  • 1 <= words[i].length <= 10
  • words[i] consists of only lowercase English letters.
  • 0 <= left <= right < words.length

Solution

Method 1 – Simple Iteration and Vowel Check

Intuition

A string is a vowel string if it starts and ends with a vowel. We can simply check each word in the given range and count how many satisfy this property.

Approach

  1. Define a set of vowels: {'a', 'e', 'i', 'o', 'u'}.
  2. Iterate over the indices from left to right (inclusive).
  3. For each word, check if its first and last character are both vowels.
  4. Count and return the number of such words.

Code

C++
class Solution {
public:
    int vowelStrings(vector<string>& words, int left, int right) {
        auto isVowel = [](char c) {
            return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
        };
        int ans = 0;
        for (int i = left; i <= right; ++i) {
            if (isVowel(words[i][0]) && isVowel(words[i].back())) ++ans;
        }
        return ans;
    }
};
Go
func vowelStrings(words []string, left int, right int) int {
    isVowel := func(c byte) bool {
        return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u'
    }
    ans := 0
    for i := left; i <= right; i++ {
        w := words[i]
        if isVowel(w[0]) && isVowel(w[len(w)-1]) {
            ans++
        }
    }
    return ans
}
Java
class Solution {
    public int vowelStrings(String[] words, int left, int right) {
        Set<Character> vowels = Set.of('a','e','i','o','u');
        int ans = 0;
        for (int i = left; i <= right; i++) {
            String w = words[i];
            if (vowels.contains(w.charAt(0)) && vowels.contains(w.charAt(w.length()-1))) ans++;
        }
        return ans;
    }
}
Kotlin
class Solution {
    fun vowelStrings(words: Array<String>, left: Int, right: Int): Int {
        val vowels = setOf('a','e','i','o','u')
        var ans = 0
        for (i in left..right) {
            val w = words[i]
            if (w.first() in vowels && w.last() in vowels) ans++
        }
        return ans
    }
}
Python
class Solution:
    def vowelStrings(self, words: list[str], left: int, right: int) -> int:
        vowels = {'a','e','i','o','u'}
        ans = 0
        for i in range(left, right+1):
            w = words[i]
            if w[0] in vowels and w[-1] in vowels:
                ans += 1
        return ans
Rust
impl Solution {
    pub fn vowel_strings(words: Vec<String>, left: i32, right: i32) -> i32 {
        let vowels = [b'a', b'e', b'i', b'o', b'u'];
        let mut ans = 0;
        for i in left..=right {
            let w = words[i as usize].as_bytes();
            if vowels.contains(&w[0]) && vowels.contains(&w[w.len()-1]) {
                ans += 1;
            }
        }
        ans
    }
}
TypeScript
class Solution {
    vowelStrings(words: string[], left: number, right: number): number {
        const vowels = new Set(['a','e','i','o','u'])
        let ans = 0
        for (let i = left; i <= right; ++i) {
            const w = words[i]
            if (vowels.has(w[0]) && vowels.has(w[w.length-1])) ans++
        }
        return ans
    }
}

Complexity

  • ⏰ Time complexity: O(n * m) where n is the number of words in the range and m is the average word length (for string indexing).
  • 🧺 Space complexity: O(1) as only a few variables and a set are used.

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