Substring Problem

• Use two pointers, i and j, both of them start from the beginning
• j is the end, i is the begin

This is the logic:

Start from j and move it one step at a time from left to right
if the i - j substring meets the requirements check whether substring is the maximum
if the i - j substring not meet the requirements, move i and then keep checking

Please see the template,

https://leetcode.com/problems/find-all-anagrams-in-a-string/discuss/92007/Sliding-Window-algorithm-template-to-solve-all-the-Leetcode-substring-search-problem.

following is the example of 159. Longest Substring with At Most Two Distinct Characters

class Solution(object):
    def lengthOfLongestSubstringTwoDistinct(self, s):
        """
        :type s: str
        :rtype: int
        """
        table = collections.Counter()
        begin = 0
        end = 0
        counter = 0
        maximum = 0


        while end < len(s):
            c = s[end]

            table[c] += 1
            if table[c] == 1:
                counter += 1

            end += 1

            while counter > 2:
                c = s[begin]
                table[c] -= 1
                if table[c] == 0:
                    counter -= 1
                begin += 1

            maximum = max(end-begin, maximum)

        return maximum