<p>Given a string <code>s</code> and an integer <code>k</code>, return <em>the maximum number of vowel letters in any substring of </em><code>s</code><em> with length </em><code>k</code>.</p>

<p><strong>Vowel letters</strong> in English are <code>&#39;a&#39;</code>, <code>&#39;e&#39;</code>, <code>&#39;i&#39;</code>, <code>&#39;o&#39;</code>, and <code>&#39;u&#39;</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;abciiidef&quot;, k = 3
<strong>Output:</strong> 3
<strong>Explanation:</strong> The substring &quot;iii&quot; contains 3 vowel letters.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;aeiou&quot;, k = 2
<strong>Output:</strong> 2
<strong>Explanation:</strong> Any substring of length 2 contains 2 vowels.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;leetcode&quot;, k = 3
<strong>Output:</strong> 2
<strong>Explanation:</strong> &quot;lee&quot;, &quot;eet&quot; and &quot;ode&quot; contain 2 vowels.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 10<sup>5</sup></code></li>
	<li><code>s</code> consists of lowercase English letters.</li>
	<li><code>1 &lt;= k &lt;= s.length</code></li>
</ul>

class Solution {
public:
    bool isVowel(char c)
    {
        return c=='a'||c=='e'|| c=='i'|| c=='o'||c=='u';
    }
    int maxVowels(string s, int k) {
        int i=0;
        int size = s.size();
        int j=k-1;
        int cnt = 0;
        for(int m=i;m<=j;m++)
        {
            if(isVowel(s[m]))
            {
                cnt++;
            }
        }

        int max_cnt = cnt;
        for(int m=j+1;m<size;m++)
        {
            i++;
            if(isVowel(s[i-1]))
            {
                cnt--;
            }
            if(isVowel(s[m]))
            {
                cnt++;
            }
            max_cnt=max(max_cnt,cnt);
        }
        return max_cnt;
        
    }
};
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