424. Longest Repeating Character Replacement

longest-repeating-character-replacement.go

// https://leetcode.com/problems/longest-repeating-character-replacement/
//
// Time: O(n)
// Space: O(1)
//
// n = number of letters in string

// .................... //

func characterReplacement(s string, k int) int {
    n := len(s)
    res := 0

    letters := [26]int{}
    maxfreq := 0
    l, r := 0, 0
    for r < n {
        ridx := s[r] - 'A'
        letters[ridx]++
        maxfreq = max(maxfreq, letters[ridx])

        subs := (r - l + 1) - maxfreq

        if subs > k {
            lidx := s[l] - 'A'
            letters[lidx]--
            l++
        }

        res = max(res, r - l + 1)
        r++
    }

    return res
}