LeetCode-Longest Substring Without Repeating Characters

原题：

Given a string, find the length of the longest substring without
repeating characters.

Examples:
Given “abcabcbb”, the answer is “abc”, which the length is 3.
Given “bbbbb”, the answer is “b”, with the length of 1.
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.

可以利用set容器，注意此题容易出错的地方是：当发现有重复字符时，不是从这个重复字符开始重新计数，而是从原有字符串中被删掉的字符开始往后计。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        set<char> t;
        int l=0,r=0,length=0;
        while(r<s.size()){
            if(t.find(s[r])==t.end()){
                t.insert(s[r++]);
                length=max(length,(int)t.size());
            }
            else{
                t.erase(s[l++]);
            }
        }
        return length;
    }
};