【leetcode】3. Longest Substring Without Repeating Characters

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

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.


使用一个变量记录子字符串的左端点，注意当字符重复时长度的变化。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int left = 0,res = 0,curRes = 0;
        vector<int> pos(256,-1);
        for(int i=0;i<s.size();i++){
            if(pos[s[i]]==-1 || pos[s[i]]<left){
                curRes++;              
                pos[s[i]] = i;
            }
            else{
                curRes = curRes-(pos[s[i]]-left);  //当前长度需要更新，减去left右移的距离
                left = pos[s[i]]+1;  
                pos[s[i]] = i;               
            }
            res = curRes>res?curRes:res;
        }
        return res;
    }
};