# Leetcode 424 Longest Repeating Character Replacement

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

Return the length of the longest substring containing the same letter you can get after performing the above operations.

```
Input: s = "ABAB", k = 2
Output: 4
Explanation: Replace the two 'A's with two 'B's or vice versa.
```

```
Input: s = "AABABBA", k = 1
Output: 4
Explanation: Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.
```

```
class Solution:
def characterReplacement(self, s: str, k: int) -> int:
count = {}
res = 0
l = 0
for r in range(len(s)):
count[s[r]] = 1 + count.get(s[r],0)
while(r-l+1)-max(count.values())>k:
count[s[l]] -=1
l += 1
res = max(res,r-l+1)
return res
```