<p>You are given a string <code>s</code> and an integer <code>k</code>. You can choose any character of the string and change it to any other uppercase English character. You can perform this operation at most <code>k</code> times.</p>

<p>Return <em>the length of the longest substring containing the same letter you can get after performing the above operations</em>.</p>

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

<pre>
<strong>Input:</strong> s = &quot;ABAB&quot;, k = 2
<strong>Output:</strong> 4
<strong>Explanation:</strong> Replace the two &#39;A&#39;s with two &#39;B&#39;s or vice versa.
</pre>

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

<pre>
<strong>Input:</strong> s = &quot;AABABBA&quot;, k = 1
<strong>Output:</strong> 4
<strong>Explanation:</strong> Replace the one &#39;A&#39; in the middle with &#39;B&#39; and form &quot;AABBBBA&quot;.
The substring &quot;BBBB&quot; has the longest repeating letters, which is 4.
There may exists other ways to achieve this answer too.</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 only uppercase English letters.</li>
	<li><code>0 &lt;= k &lt;= s.length</code></li>
</ul>

class Solution {
    int characterReplacement_Brute(string s, int k) {
        int maxLen = 0;
        int n = s.size();
        for(int i = 0; i < n; i++){
            int maxFreq = 0;
            int hash[26]{0};
            for(int j = i; j < n; j++){
                hash[s[j] - 'A']++;
                maxFreq = max(maxFreq, hash[s[j] - 'A']);
                int changes = (j - i + 1) - maxFreq;
                if(changes <= k)
                    maxLen = max(maxLen, j - i + 1);
                else
                    break;
            }
        }
        return maxLen;
    }
    int characterReplacement_SlidingWindow(string s, int k) {
        int maxFreq = 0;
        int hash[26]{0};
        int maxLen = 0;
        int n = s.size();
        int i = 0, j = 0;
        while(j < n){
            hash[s[j] - 'A']++;
            maxFreq = max(maxFreq, hash[s[j] - 'A']);
            while( (j - i + 1) - maxFreq > k ){
                hash[s[i] - 'A']--;
                maxFreq = 0;
                for(int k = 0; k < 26; k++){
                    maxFreq = max(maxFreq, hash[k]);
                }
                i++;
            }
            if( (j - i + 1) - maxFreq <= k ){
                maxLen = max(maxLen, (j - i + 1));
            }
            j++;
        }
        return maxLen;
    }
public:
    int characterReplacement(string s, int k) {
        return characterReplacement_SlidingWindow(s, k);
    }
};
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