159. Longest Substring with At Most Two Distinct Characters

Given a string, find the length of the longest substring T that contains at most 2 distinct characters.

For example, Given s = "eceba",

T is "ece" which its length is 3.

Solution: HashMap

import collections


class Solution(object):
    def lengthOfLongestSubstringKDistinct(self, s, k):
        """
        :type s: str
        :type k: int
        :rtype: int
        """
        max_len = 0
        count = collections.defaultdict(int)
        slow = 0
        for fast, char in enumerate(s):
            count[char] += 1
            while len(count) > k:
                left = s[slow]
                count[left] -= 1
                if count[left] == 0:
                    del count[left]
                slow += 1
            max_len = max(max_len, fast - slow + 1)
        return max_len