Leetcode3.无重复字符的最长子串(中等)Python

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        if len(s)==0:
            return 0
        if len(s)==1:
            return 1
        else:
            result=''
            result+=s[0]
            max_length=[]
            for i in range(len(s)-1):
                for j in range(i+1,len(s)):
                    if s[j] not in result:
                        result+=s[j]
                    else:
                        break
                length=len(result)
                max_length.append(length)
                result=''
                result+=s[i+1]
            return max(max_length)

写得够烂的哈哈

知识点：

 字符串没有append的概念，如果要合并在一起用+。

优化代码：

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        #" "
        #Expected Output:1
        #max=i-start=0-start=1 start=-1
        #d={'a':0,'b':1,...} value=index
        start=-1
        max=0
        d={}
        for i in range(len(s)):
            if s[i] in d and d[s[i]]>start:
                start=d[s[i]]
                d[s[i]]=i#重新赋值
            else:#s[i] not in d
                d[s[i]]=i#写在dict里面
                if i-start>max:
                    max=i-start
        return max 

 分析 if s[i] in d and d[s[i]]>start:中的 d[s[i]]>start

测试代码：s="tmmzuxt"

（1）有d[s[i]]>start:

 （2）没有d[s[i]]>start: