Maximum Number of Vowels in a Substring of Given Length [Medium]

Input: s="abciiidef", k=3 → Output: 3 ("iii")
Input: s="aeiou", k=2     → Output: 2

int maxVowels(string s, int k) {
    string v="aeiou";
    auto isV=[&](char c){return v.find(c)!=string::npos;};
    int cnt=0, ans=0;
    for(int i=0;i<k;i++) cnt+=isV(s[i]);
    ans=cnt;
    for(int i=k;i<s.size();i++){cnt+=isV(s[i])-isV(s[i-k]);ans=max(ans,cnt);}
    return ans;
}

public int maxVowels(String s, int k) {
    Set<Character> v=Set.of('a','e','i','o','u');
    int cnt=0, ans=0;
    for(int i=0;i<k;i++) if(v.contains(s.charAt(i)))cnt++;
    ans=cnt;
    for(int i=k;i<s.length();i++){
        if(v.contains(s.charAt(i)))cnt++;
        if(v.contains(s.charAt(i-k)))cnt--;
        ans=Math.max(ans,cnt);
    }
    return ans;
}

def maxVowels(s: str, k: int) -> int:
    vowels = set('aeiou')
    cnt = sum(c in vowels for c in s[:k])
    ans = cnt
    for i in range(k, len(s)):
        cnt += (s[i] in vowels) - (s[i-k] in vowels)
        ans = max(ans, cnt)
    return ans