12-Count-Vowel-Substrings.md

Count Vowel Substrings

Problem Link

https://leetcode.com/problems/count-vowel-substrings/

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Pattern

• Sliding Window

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Approach

For each position, expand window to include all vowels; count substrings ending at each vowel.

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Time Complexity

O(n)

Space Complexity

O(1)

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Java Solution

class Solution {
    public int countVowelSubstrings(String word) {
        int ans = 0, left = 0;
        String vowels = "aeiou";
        for (int right = 0; right < word.length(); right++) {
            if (!vowels.contains(String.valueOf(word.charAt(right)))) left = right + 1;
            else ans += right - left + 1;
        }
        return ans;
    }
}