Leetcode119: Longest Substring Without Repeating Characters

最新推荐文章于 2025-09-11 19:19:55 发布

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本文介绍了一种求解字符串中最长无重复字符子串长度的高效算法，并提供了C++及Python实现。通过历遍字符串并利用哈希表记录字符最后出现的位置，该算法能在O(n)时间内找到最长无重复子串。

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for "abcabcbb" is "abc", which the length is 3. For "bbbbb" the longest substring is "b", with the length of 1.

解题思路：

历遍字符串，当当前字符出现过的时候，子串开始位置+1，否则更新locs数组中的hash值为当前位置。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int loc[256];
        memset(loc, -1, sizeof(loc));
        int index = -1;
        int max = 0;
        for(int i = 0; i < s.length(); i++)
        {
            if(loc[s[i]] > index)
            {
                index = loc[s[i]];
            }
            if(i-index>max)
            {
                max = i-index;
            }
            loc[s[i]] = i;
        }  
        return max;
    }
};

python代码：

class Solution(object):
    def lengthOfLongestSubstring(self, s):
        """
        :type s: str
        :rtype: int
        """
        res = 0  
        left = 0  
        d = {}  
  
        for i, ch in enumerate(s):  
            if ch in d and d[ch] >= left:  
                left = d[ch] + 1  
            d[ch] = i  
            res = max(res, i - left + 1)  
        return res