Maximum Number of Vowels in a Substring of Given Length

Description

Given a string s and an integer k.

Return the maximum number of vowel letters in any substring of s with length k.

Vowel letters in English are (a, e, i, o, u).

 

Example 1:

Input: s = "abciiidef", k = 3
Output: 3
Explanation: The substring "iii" contains 3 vowel letters.

Example 2:

Input: s = "aeiou", k = 2
Output: 2
Explanation: Any substring of length 2 contains 2 vowels.

Example 3:

Input: s = "leetcode", k = 3
Output: 2
Explanation: "lee", "eet" and "ode" contain 2 vowels.

Example 4:

Input: s = "rhythms", k = 4
Output: 0
Explanation: We can see that s doesn't have any vowel letters.

Example 5:

Input: s = "tryhard", k = 4
Output: 1

 

Constraints:

• 1 <= s.length <= 10^5
• s consists of lowercase English letters.
• 1 <= k <= s.length

Solution(javascript)

/**
 * @param {string} s
 * @param {number} k
 * @return {number}
 */
const maxVowels = function (s, k) {
  const map = {
    a: true,
    e: true,
    i: true,
    o: true,
    u: true,
  }
  let count = 0
  let currentLength = 0
  let max = 0
  for (let i = 0; i < s.length; i++) {
    const c = s[i]
    currentLength += 1
    if (map[c]) {
      count += 1
    }

    if (currentLength > k) {
      const firstC = s[i - k]
      if (map[firstC]) {
        count -= 1
      }
      currentLength -= 1
    }
    max = Math.max(max, count)
  }
  return max
}