Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

思路

1. 遍历字符串，过程中将出现过的字符存入字典，key为字符，value为字符下标
2. 用maxLength保存遍历过程中找到的最大不重复子串的长度
3. 用start保存最长子串的开始下标
4. 如果字符已经出现在字典中，更新start的值
5. 如果字符不在字典中，更新maxLength的值
6. return maxLength

代码

class Solution:
    def lengthOfLongestSubstring(self, s: str) -> int:
        start = maxLength = 0
        charSeq = {}
        for i in range(len(s)):
            if s[i] in charSeq and start <= charSeq[s[i]]:
                start = charSeq[s[i]] + 1
            else:
                maxLength = max(maxLength, i - start + 1)
            charSeq[s[i]] = i
        return maxLength