3. Longest Substring Without Repeating Characters

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思路：begin（最重要的变量）记录longest substring开始的位置；longest当前substring的长度；map存放字符的index。实质上是维护了一个substring区间，使得substring内的所有字符都是独一无二的。

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class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        if (s.length() <= 1){
            return s.length();
        }
        unordered_map<char, int> map;
        int ans = 0;
        int longest = 0;
        int begin = 0;
        for (int i = 0; i < s.length(); ++i){
            if (map.count(s[i]) == 0 || map[s[i]] < begin){ // 只要map中的字符index不在begin之后，都视为不存在
                map[s[i]] = i;
                ++longest;
            }else{
                int before = map[s[i]];
                map[s[i]] = i;
                longest = i - before;
                begin = before + 1;
            }
            
            if (longest > ans){
                ans = longest;
            }
        }
        
        return ans;
    }
};

来源：CSDN

作者：zxc120389574

链接：https://blog.csdn.net/zxc120389574/article/details/104111719