CountVowelsStringInRanges.java

class Solution {
    public int[] vowelStrings(String[] words, int[][] queries) {
        int n = words.length;
        int prefixSum[] = new int[n];
        prefixSum[0] = isVowel(words[0]);
        for(int i=1;i<n;i++){
            prefixSum[i] = prefixSum[i-1] + isVowel(words[i]);
        }
        int m = queries.length;
        int ans[] = new int[m];
        for(int i=0;i<m;i++){
            int l = queries[i][0];
            int r = queries[i][1];
            int res = prefixSum[r]; 
            if(l!=0){
                res-= prefixSum[l-1];
            }
            ans[i] = res;
        }
        return ans;
    }

    public int isVowel(String word){
        HashSet<Character> set = new HashSet<>(Arrays.asList('a','e','i','o','u'));
        char first = word.charAt(0);
        char last = word.charAt(word.length()-1);
        if(set.contains(first) && set.contains(last)){
            return 1;
        }
        return 0;
    }
}