Count Vowel Substrings of a String LeetCode solution in C++

1
class Solution {
2
 public:
3
  bool isVowel(char c) {
4
    return c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u';
5
  };
6

7
  int atMostK(string &s, int k) {
8
    int res = 0, i = 0, n = s.size();
9
    unordered_map<char, int> mp;
10

11
    for (int j = 0; j < n; j++) {
12
      if (!isVowel(s[j])) {
13
        i = j + 1;
14
        // Clear map as new substring will begin
15
        mp.clear();
16
        continue;
17
      }
18
      mp[s[j]]++;
19
      while (mp.size() > k) {
20
        mp[s[i]]--;
21
        if (mp[s[i]] == 0) mp.erase(s[i]);
22
        i++;
23
      }
24
      res += j - i + 1;
25
    }
26
    return res;
27
  }
28

29
  int countVowelSubstrings(string str) {
30
    return atMostK(str, 5) - atMostK(str, 4);
31
  }
32
};