# 424. Longest Repeating Character Replacement

Medium
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.
Example 1:
Input: s = "ABAB", k = 2
Output:
4
Explanation:
Replace the two 'A's with two 'B's or vice versa.
Example 2:
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.
Constraints:
• `1 <= s.length <= 105`
• `s` consists of only uppercase English letters.
• `0 <= k <= s.length`

### 解題

Runtime: 0 ms, faster than 100.00%
Memory Usage: 2.5 MB, less than 78.65%
func characterReplacement(s string, k int) int {
count := make([]int, 26)
maxCount := 0
maxLength := 0
left := 0
for right:= 0; right < len(s); right++ {
count[s[right]-'A']++
maxCount = max(maxCount, count[s[right]-'A'])
for left<=right && right-left+1-maxCount > k {
count[s[left]-'A']--
left++
}
maxLength = max(maxLength, right - left + 1)
}
return maxLength
}
func max(a, b int) int {
if a > b { return a }
return b
}