题目链接：

题目：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：维护一个窗口，每次关注窗口中的字符串，维护一个HashSet，每扫描一个字符，如果HashSet中包含该字符，则移动左边窗口至重复字符的下一个字符，如果HashSet中没有改字符，则移动右边窗口。时间负复杂度为O(n)，空间复杂度也为O(n)。具体代码如下：

public class Solution{    public static void main(String[] args)    {        String str="abcbbc";        System.out.println(lengthOfLongestSubstring(str));    }    public static int lengthOfLongestSubstring(String s)     {         if(s==null && s.length()==0)                return 0;            HashSet
     
       set = new HashSet
      
       ();            int max = 0;     //最大不重复字符串长度            int left = 0;     //不重复字符串起始位置            int right = 0;    //不重复字符串结束为止            while(right