【leetcode】1456. Maximum Number of Vowels in a Substring of Given Length

题目如下：

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

解题思路：滑动窗口的问题。

代码如下：

class Solution(object):
    def maxVowels(self, s, k):
        """
        :type s: str
        :type k: int
        :rtype: int
        """
        res = 0
        count = 0
        vowel = ['a','e','i','o','u']
        for i in range(len(s)):
            if i < k:
                if s[i] in vowel:
                    count += 1
            elif i >= k:
                if s[i] in vowel:
                    count += 1
                if s[i-k] in vowel:
                    count -= 1
            res = max(res,count)
        return res