003Longest Substring Without Repeating Characters

Given "pwwkew", 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.

求最长子字符串的长度，注意是连续的子字符串。双指针维护一个动态窗口，遍历一个长度即可，时间复杂度O(n)，用一个hashSet判断动态窗口中是否能加上，即字母是否重复，遍历一圈后记录最大的窗口长度。

看了讨论区的代码，思路是一样的，只不过用的是hashMap记录是否重复，看起来简洁一些

代码：

class Solution {    public int lengthOfLongestSubstring(String s) {        int left = 0, right = 0, max = 0;if (s == null || s.length() == 0) {return 0;}Set<Character> set = new HashSet<>();while (right < s.length()) {                        //能添加上 没有重复，右指针走一个while (right < s.length() && set.add(s.charAt(right))) {right++;}max = Math.max(max, right - left);set.remove(s.charAt(left));            //有重复的话向左移，直到重复字符被剔除 移动到了下一个字母位置left++;}return max;    }}