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

使用到 window sliding 的技巧

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
}