[ leetcode ] Longest Substring with At Most Two Distinct Characters

https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/
最近のアルゴリズムは全く解けず,久しぶりにループコードを開いた.
まだ問題があります.

Longest Substring with At Most Two Distinct Characters

問題の説明は以下の通りです.
2つの文字だけからなる最長連続部分文字列の長さを求めます.
問題を見て、白俊回転寿司問題を思い出し、カトピラー法で解いた.
https://codility.com/media/train/13-CaterpillarMethod.pdf
以上のリンクは,この方法に関するpdfである.勉強すれば広く応用できる.

import collections


class Solution:

    def lengthOfLongestSubstringTwoDistinct(self, s: str) -> int:
        start = 0
        end = 0

        letterCounter = collections.defaultdict(int)
        letterKey = set()
        answer = 0
        cur_string = collections.deque([])

        def addLetter(value):
            letterCounter[value] += 1
            letterKey.add(value)

        def deleteLetter(value):
            if letterCounter[value] == 1:
                letterKey.remove(value)
            letterCounter[value] -= 1

        def isAddable(value):
            return any([
                value in letterKey and len(letterKey) <= 2,
                value not in letterKey and len(letterKey) < 2
            ])

        while (start < len(s) and end < len(s)):
            if isAddable(s[end]):
                addLetter(s[end])
                cur_string.append(s[end])
                answer = max(answer, len(cur_string))
                end += 1
            else:
                deleteLetter(s[start])
                cur_string.popleft()
                start += 1
        return answer