Leetcode 3. Longest Substring Without Repeating Characters

最新推荐文章于 2025-05-18 01:04:12 发布

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最新推荐文章于 2025-05-18 01:04:12 发布

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本文介绍了一种高效算法，用于求解给定字符串中最长的无重复字符子串长度。通过滑动窗口方法和哈希映射实现，示例包括abcabcbb等，解析了关键步骤和边界条件。

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link:https://leetcode.com/problems/longest-substring-without-repeating-characters/description/

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

Example 1:

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

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        maxlen=0
        d={}
        start=0
        
        for i,c in enumerate(s):
            if c not in d or d[c]<start :
                maxlen=max(maxlen,i+1-start)
            else:
                start=d[c]+1
            d[c]=i
        return maxlen

用一个map记录字符的下标，类似于滑动窗口的方法来记录，以abcabcbb为例，当滑动到第二个a的时候更新start的位置，将第一个a从记录中去除。

注意d[c]<start是必要的，如tmmzuxt中，当到第二个t的时候，d[t]=0,而此时start已经更新到了后面，如果没有这个判断就不会把第二个t包括进最大长度中了