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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] = [l<sub>i</sub>, r<sub>i</sub>] asks us to find the number of strings present in the range l<sub>i</sub> to r<sub>i</sub> (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'.

Example 1:

Input: words = ["aba","bcb","ece","aa","e"], queries = [[0,2],[1,4],[1,1]]
Output: [2,3,0]
Explanation: The strings starting and ending with a vowel are "aba", "ece", "aa" and "e".
The answer to the query [0,2] is 2 (strings "aba" and "ece").
to query [1,4] is 3 (strings "ece", "aa", "e").
to query [1,1] is 0.
We return [2,3,0].

Example 2:

Input: words = ["a","e","i"], queries = [[0,2],[0,1],[2,2]]
Output: [3,2,1]
Explanation: Every string satisfies the conditions, so we return [3,2,1].
class Solution {
public:
    vector<int> vowelStrings(vector<string>& words, vector<vector<int>>& queries) {
        vector<int> prefixSum(words.size()+1,0);
        vector<int> result;

        function<bool(char)> isVowel = [](char ch)->bool{
            if( ch == 'a' || ch == 'e' || ch =='i' || ch == 'o' || ch=='u'){
                return true;
            }

            return false;
        };

        int index = 1;
        for( string str:words){
            if( isVowel(str.front()) && isVowel(str.back()) ){
                prefixSum[index] = prefixSum[index-1]+1;
            } else
                prefixSum[index] = prefixSum[index-1];

            index++;
        }
 

        for( auto q: queries ){
          result.push_back( prefixSum[q[1]+1] - prefixSum[q[0]] );
        }

        return result;
    }
};