1456. Maximum Number of Vowels in a Substring of Given Length

max-vowels-substring.js

const VOWELS = ['a', 'e', 'i', 'o', 'u'];

/**
 * @param {string} str
 * @param {number} frameSize
 * @return {number}
 */
var maxVowels = function(str, frameSize) {
  // Given a char return true if it's a vowel
  const isVowel = (char) => VOWELS.includes(char);

  const arr = Array.from(str);

  let currentCount = arr.slice(0, frameSize).filter(isVowel).length;
  let maxVowelsCount = currentCount;

  for (let i = 1; i <= arr.length - frameSize; ++i) {
    const leftSide = arr[i - 1];
    const rightSide = arr[i + (frameSize - 1)];

    if (isVowel(leftSide)) {
      currentCount--;
    }

    if (isVowel(rightSide)) {
      currentCount++;
    }

    if (currentCount > maxVowelsCount) {
      maxVowelsCount = currentCount;
    }
  }

  return maxVowelsCount;
}