题目
参考《算法小抄》重的解法，重点理解！！！

class Solution {public int lengthOfLongestSubstring(String s) {if (s.length() < 2) {return s.length();}char[] array = s.toCharArray();int left = 0, right = 0, res = 0;int[] count = new int[256];while (right < array.length) {char cur = array[right];++right;++count[cur];while (count[cur] > 1) {char d = array[left];++left;--count[d];}res = Math.max(res, right - left);}return res;}
}