Leetcode: Longest Substring with At Most Two Distinct Characters

Question

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.

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Solution

Get idea from here1, here2

Using sliding window method

class Solution(object):
    def lengthOfLongestSubstringTwoDistinct(self, s):
        """ :type s: str :rtype: int """

        s = list(s)

        start, res = 0,0
        dict_c = {}
        for cur,c in enumerate(s):
            if c in dict_c:
                dict_c[c] += 1
            else: 
                # new char
                while len(dict_c.keys())>1:    # make sure there is only one char in the window before c
                    if dict_c[ s[start] ]==1:
                        del dict_c[ s[start] ]
                    else:
                        dict_c[ s[start] ] -= 1
                    start += 1

                dict_c[c] = 1

            res = max(res, cur-start+1)  # have to update res no matter what happens

        return res