[leetcode] longest substring without repeating characters

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：遍历字符串，当遇到重复的字符时，要更新无重复子串的左边界，比如abcabcbb, 遍历abca时都没有问题，这是也不断得更新最大无重复子串的长度，当比例到s[4]时，遇到了重复的b，由于不能有重复的b，前开始的ab都不能在新的子串里，所以把left左边界更新至s[2]，and so forth。

public class Solution {    public int lengthOfLongestSubstring(String s) {        HashSet<Character> set = new HashSet<Character>();        int max = 0;        int left = 0;        for(int i = 0; i < s.length(); i++){            if(set.contains(s.charAt(i))){                while(left < i && s.charAt(left) != s.charAt(i)){                    set.remove(s.charAt(left));                    left++;                }                left++;            }else{                set.add(s.charAt(i));                max = Math.max(max, i - left + 1);            }        }        return max;    }}