leetcode 3. Longest Substring Without Repeating Characters

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        
         boolean []arr = new boolean[256];
         for(int i = 0; i < 256; i++)
         {
             arr[i] = false;
         }
         
         int a = 0;//记录开始位置
         int b = 0;//记录子串的结束位置 
         int maxlength = 0;
         
         while(b < s.length())
         {
             if(!arr[s.charAt(b)])
             {
                 arr[s.charAt(b)] = true;// 访问过了 
                 b++;
             }
             
             else
             {
                 while(s.charAt(a) != s.charAt(b))
                 {
                     arr[s.charAt(a)] = false;
                     a++;
                 }
                 
                 a++;
                 b++;
                 
             }
             
             maxlength = (maxlength > (b-a))? maxlength:(b-a);
         }
         
         return maxlength;
        
        
    }
}