[LeetCode] 3. Longest Substring Without Repeating Characters

题目：https://leetcode.com/problems/longest-substring-without-repeating-characters/description/

题目描述

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.

方法：

先设立一个哈希，对于每个字符存入上次出现的位置，设立两个字符指针，两指针都在-1处，由右指针向向右扫描，每扫描一个，将该字符对应的哈希表中的值改为当前的位置，将该值与左指针位置比较，若该值大于左指针，将左指针赋值为该值，计算出两指针间 即字符串长度，判断该值是否为最大的字符串长度，即该串是否为最大字符。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        vector<int> dict(256,-1);
        int maxlen=0,start=-1;
        for(int i = 0;i<s.length();i++){
            if(dict[s[i]]>start){
                start = dict[s[i]];
            }
            dict[s[i]] = i;
            maxlen = max(maxlen,i-start);
        }
        return maxlen;
        
    }
};