15. 1456. Maximum Number of Vowels in a Substring of Given Length

class Solution {
    public int maxVowels(String s, int k) {
        int cnt =0;
        int maxCnt = 0;
        int start = 0,end =0;
        while(end<s.length()){
            //expansion
            if(checkVowel(s.charAt(end++))){
                cnt++;
            }

            while(start<end && end-start>k){
                 if(checkVowel(s.charAt(start++))){
                    cnt--;
                 }
            }

              maxCnt = Math.max(cnt,maxCnt);
        }
        return maxCnt;
        
    }

    public boolean checkVowel(char ch){
        if(ch=='a'||ch=='e'||ch=='i'||ch=='o'||ch=='u'){
            return true;
        }
        return false;
    }
}