【LeetCode】Longest Substring Without Repeating Characters

最新推荐文章于 2025-05-18 01:04:12 发布

xiaozhuaixifu

最新推荐文章于 2025-05-18 01:04:12 发布

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分类专栏： LeetCode 文章标签： hash

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本文介绍了一种使用哈希表解决字符串中无重复字符最长子串问题的方法，通过遍历字符串并更新子串长度，实现高效求解。

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题目描述：

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.

思路：用hashtable来标记每个字符出现的位置

代码：

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(s.size() == 0) return 0;
        int cnt=0;
        int hash[256];
        int maxlen=-1;
        memset(hash,-1,sizeof(hash));
        
        for(int i=0; i<s.size(); i++)
        {
            char ch = s[i];
            if(hash[ch] == -1)
            {
                cnt++;
                hash[ch] = i;
                maxlen = max(maxlen,cnt);
            }
            else 
            {
               int index = hash[ch];
               //cnt = i-index;
               for(int j=i-cnt; j<=index; j++)
               {
                   hash[s[j]] = -1;
               }
               cnt = i-index;
               hash[ch]=i;
               maxlen = max(maxlen,cnt);
            }
        }
        return maxlen;
    }
};