滑动窗口法
class Solution {
public:int lengthOfLongestSubstring(string s) {int left = 0;int right = 0;int maxlen = 0;set<char> window;while(right < s.size()){while(window.find(s[right]) != window.end()){window.erase(s[left]);left++;}maxlen = max(maxlen, right-left+1);window.insert(s[right++]);}return maxlen;}
};