一、题目

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

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’, and ‘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.

Constraints:

1 <= s.length <= 105
s consists of lowercase English letters.
1 <= k <= s.length

二、题解

利用滑动窗口进行判断

class Solution {
public:
    int maxVowels(string s, int k) {
        int n = s.length();
        unordered_map<char,int> map;
        map['a'] = 1;
        map['e'] = 1;
        map['i'] = 1;
        map['o'] = 1;
        map['u'] = 1;
        int count = 0;
        int res = 0;
        for(int i = 0;i < k;i++){
            if(map[s[i]] == 1) count++;
        }
        res = max(res,count);
        for(int i = k;i < n;i++){
            if(map[s[i - k]] == 1) count--;
            if(map[s[i]] == 1) count++;
            res = max(res,count);
        }
        return res;
    }
};