[leetcode]3. Longest Substring Without Repeating Characters

只要注意点最长非重复字串出现在字符串末尾的情况就好，挺简单的。（时间和内存都惨不忍睹）

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        string = s
        #---
        #lenth = 1
        if string == "":
            return 0
        if len(string) == 1:
            return 1
        # # ---
        # find substring
        longestSubstring = 0
        for start in range(len(string)):
            for end in range(start +1 , len(string)):
                if string[end] not in string[start:end]:  # find whether current letter duplication
                    #---
                    #check if there have letter after end
                    #careful with the letter string[end]
                    if end +1 == len(string):
                        if (end - start +1) > longestSubstring:
                            return (end - start +1)
                        else:
                            return longestSubstring
                else:
                    if len(string[start:end])  > longestSubstring:
                        longestSubstring = len(string[start:end])
                    break
        return longestSubstring