#1456 - Maximum Number of Vowels in a Substring of Given Length

MediumSliding Window

Given a string s and an integer k, return the maximum number of vowel letters (a, e, i, o, u) in any substring of s with length k.

Input	Output
s = "abciiidef", k = 3	3
s = "aeiou", k = 2	2
s = "leetcode", k = 3	2

Solution Space

Try it

/**
 * Finds the maximum number of vowels in any substring of length k.
 *
 * @param s Source string of lowercase letters
 * @param k Window size
 * @returns Maximum vowel count in any k-length substring
 */
export function maxVowels(s: string, k: number): number {
  const vowels = new Set(["a", "e", "i", "o", "u"]);

  let count = 0;
  for (let i = 0; i < k; i++) {
    if (vowels.has(s[i])) count++;
  }

  let max = count;

  for (let i = k; i < s.length; i++) {
    if (vowels.has(s[i])) count++;
    if (vowels.has(s[i - k])) count--;
    if (count > max) max = count;
  }

  return max;
}

Approach: fixed-size sliding window – maintain a window of size k, updating the count of vowels by adding the new element and subtracting the old element as the window slides.

Time: O(n) – single pass after the initial window; `Set.has` is O(1) for a 5-element set.

Space: O(1) – the vowel set is constant-size (5 elements), plus a few counters.

#1004 Max Consecutive Ones III

#1493 Longest Subarray of 1's After Deleting One Element