LeetCode-3. Longest Substring Without Repeating Characters

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.

思路：

滑动窗：

1、定义一个空set，用来保存遍历到的字符；

2、从头遍历字符串，将遍历到的字符与set中的元素比较，若set中没有该元素，则将窗体右侧右移一位，并更新最长子串的值；若set中有该元素，则将此元素删除，将窗体左侧左移一位；

3、重复步骤2，直到到达字符串末尾。

时间复杂度：O(n)

class Solution {public:    int lengthOfLongestSubstring(string s) {        if(s.empty())            return 0;        int i=0,j=0,res=0;        int n=s.size();        set<int> mySet;        while(i<n&&j<n)        {            if(mySet.count(s[j])==0)            {                mySet.insert(s[j]);                j++;                res=max(res,j-i);            }            else            {                mySet.erase(s[i]);                i++;            }        }        return res;    }};