Maximum Number Of Vowels In A Substring

In this blog, you will learn how to find the maximum number of vowels in a substring.

Introduction

 

Given a string s and an integer k, return the maximum number of vowel letters in any substring of s with length k. Note that vowel letters in English are [ a, e, i, o, u ]. So let's take an example where s is "abciiidef" and k is 3. so the output will be 3 because the substring "iii" contains 3 vowel letters in the string s. Given below are some more examples:

static void Main(string[] args)
{
    var result = MaxVowels("abciiidef", 3);
    // example 1 : result = 3
    result = MaxVowels("aeiou", 2);
    // example 2 : result = 2
    result = MaxVowels("leetcode", 3);
    // example 3 : result = 2
    result = MaxVowels("rhythms", 4);
    // example 4 : result = 0
    result = MaxVowels("tryhard", 4);
    // example 5 : result = 1
}

Solution

 

Our approach towards the problem will be simplest, we will have nested loops one which will substring the string s and the next will count the vowels in that substring. Here are the steps to how it's done,

1. Create a list of vowels for reference and assign [ a, e, i, o, u ].
2. Iterate from 0th to (s.Length - k)th index of the string s to get all the substrings of length k.
3. Count the vowels for every substring.
4. Compare every vowel count of substrings and return the maximum vowel count.

Here is the C# code for the algorithm given above:

public static int MaxVowels(string s, int k)
{
    int maxVowels = 0;
    List<char> vowels = new List<char> { 'a', 'e', 'i', 'o', 'u' };
    for (int i = 0; i <= s.Length - k; i++)
    {
        string substring = s.Substring(i, k);
        int countVowels = substring.Where(x => vowels.Contains(x)).Count();
        maxVowels = Math.Max(countVowels, maxVowels);
    }
    return maxVowels;
}