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# 題目敘述

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.

# Solution

class Solution {
public:
    int maxVowels(string s, int k) {
        int res = 0;
        unordered_set<char> vowels = {'a', 'e', 'i', 'o', 'u'};
        for (int i=0, tmp=0; i<s.size(); i++) {
            tmp += vowels.count(s[i]);
            if (i - k >= 0) tmp -= vowels.count(s[i-k]);
            res = max(res, tmp);
        }
        return res;
    }
};
class Solution {
    public int maxVowels(String s, int k) {
        int ans = 0;
        String temp = s.substring(0, k);
        for (char t : temp.toCharArray()) {
            if (isVowel(t)){
                ans++;
            }
        }
        int cur = ans;
        for (int i = k; i < s.length(); i++) {
            if (isVowel(s.charAt(i)))
                cur++;
            if (isVowel(s.charAt(i - k)))
                cur--;
            ans = Math.max(ans, cur);
        }
        return ans;
    }
    public boolean isVowel(char c) {
        if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
            return true;
        return false;
    }
}