Today I have done leetcode's January LeetCoding Challenge with cpp.

January LeetCoding Challenge 2

Description

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 i^th 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].

Constraints:

• 1 <= words.length <= 105
• 1 <= words[i].length <= 40
• words[i] consists only of lowercase English letters.
• sum(words[i].length) <= 3 * 105
• 1 <= queries.length <= 105
• 0 <= li <= ri < words.length

Solution

class Solution {
  const set<char> vowel = {'a', 'e', 'i', 'o', 'u'};
  bool isVowelString(const string &word) {
    return vowel.count(word.front()) && vowel.count(word.back());
  }
public:
  vector<int> vowelStrings(vector<string>& words, vector<vector<int>>& queries) {
    vector<int> prefix(words.size() + 1);
    for(int i = 0; i < words.size(); ++i) {
      prefix[i + 1] = prefix[i] + isVowelString(words[i]);
    }
    vector<int> answer;
    answer.reserve(queries.size());
    for(auto &q : queries) {
      answer.push_back(prefix[q[1] + 1] - prefix[q[0]]);
    }

    return answer;
  }
};

// Accepted
// 93/93 cases passed (4 ms)
// Your runtime beats 81.49 % of cpp submissions
// Your memory usage beats 68.33 % of cpp submissions (69.4 MB)