Problem Statement

Given a string with lowercase letters only, if you are allowed to replace no more than k letters with any letter, find the length of the longest substring having the same letters after replacement.

Example 1:

Input: str="aabccbb", k=2  
Output: 5  
Explanation: Replace the two 'c' with 'b' to have a longest repeating substring "bbbbb".

Example 2:

Input: str="abbcb", k=1  
Output: 4  
Explanation: Replace the 'c' with 'b' to have a longest repeating substring "bbbb".

Example 3:

Input: str="abccde", k=1  
Output: 3  
Explanation: Replace the 'b' or 'd' with 'c' to have the longest repeating substring "ccc".

Constraints:

• 1 <= str.length <= 10^5
• s consists of only lowercase English letters.
• 0 <= k <= s.length