2559. Count Vowel Strings in Ranges

You are given a 0-indexed array of strings words and a 2D array of integers queries.

Each query queries[i] = [li, ri] asks us to find the number of strings present in the range li to ri (both inclusive) of words that start and end with a vowel.

Return an array ans of size queries.length, where ans[i] is the answer to the ith query.

Note that the vowel letters are ‘a’, ‘e’, ‘i’, ‘o’, and ‘u’.

class Solution {
public:
    vector<int> vowelStrings(vector<string>& words, vector<vector<int>>& queries) {
        vector<int> psum{0};
        unordered_set<char> v{'a','e','i','o','u'};
        for(auto w : words) {
            int now = v.count(w.front()) and v.count(w.back());
            psum.push_back(psum.back() + now);
        }
        vector<int> res;
        for(auto q : queries) {
            int l = q[0], r = q[1];
            res.push_back(psum[r+1] - psum[l]);
        }
        return res;
    }
};