Maximum Number of Vowels in a Substring of Given Length in C++

Suppose we have a string s and an integer k. We have to find the maximum number of vowel letters in any substring of s with length k.

So, if the input is like s = "abciiidef", k = 3, then the output will be 3

To solve this, we will follow these steps −

cnt := 0
Define one set m
for each vowel v, do
- insert v into m
ret := 0
for initialize i := 0, when i < k, update (increase i by 1), do −
- cnt := cnt + (1 when s[i] is in m, otherwise 0)
ret := maximum of ret and cnt
n := size of s
for initialize i := k, when i < n, update (increase i by 1), do −
- if s[i - k] is member of m, then −
  - (decrease cnt by 1)
- cnt := cnt + (1 when s[i] is in m, otherwise 0)
- ret := maximum of ret and cnt
return ret

Example

Let us see the following implementation to get a better understanding −

Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
   int maxVowels(string s, int k) {
      int cnt = 0;
      set<char> m;
      for (auto it : { 'a', 'e', 'i', 'o', 'u' })
      m.insert(it);
      int ret = 0;
      for (int i = 0; i < k; i++) {
         cnt += m.count(s[i]) ? 1 : 0;
      }
      ret = max(ret, cnt);
      int n = s.size();
      for (int i = k; i < n; i++) {
         if (m.count(s[i - k])) {
            cnt--;
         }
         cnt += m.count(s[i]) ? 1 : 0;
         ret = max(ret, cnt);
      }
      return ret;
   }
};
main(){
   Solution ob;
   cout << (ob.maxVowels("abciiidef",3));
}