3. 无重复字符的最长子串

 

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.

 

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

### 解题思路

滑窗操作，i为右边界，left为左边界，实现效果为，i不断向右移，而左边界需要判断是否移动，判断依据为新入的元素是否存在于窗口中，若存在且比窗口左边界的指示值大则把左窗口的边界向右移动，移动依据为map中的映射。并且右移的同时不断得建立映射。而left=-1是为了指示左边界的左边一个值，所以为-1。并且存储一个res值记录大小。

 

### 代码

```cpp

class Solution {

public:

    int lengthOfLongestSubstring(string s) {

        int left=-1;int res=0;

        unordered_map<int,int> m;

        for(int i=0;i<s.size();i++)

        {

            if(m.count(s[i])&&m[s[i]]>left)

            {

            left=m[s[i]];

            }

            else

            {

            res=max(i-left,res);

            }

            m[s[i]] = i;

        }

        return res;

    }

};

参考资料:

https://www.cnblogs.com/grandyang/p/4480780.html 

https://www.cnblogs.com/ariel-dreamland/p/8668286.html   思路以及实现过程

https://blog.youkuaiyun.com/qq_34909804/article/details/103681865 map用法