leetcode Longest Substring Without Repeating Characters 最长不重复子串

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.

题意：给一个字符串，找到连续的不重复子串。

思路：使用数组来保存字符串中每个字符最后一次出现的位置

class Solution {public:    int lengthOfLongestSubstring(string s) {        if (s.empty()) return 0;        int maxl = 0, start = -1;        vector<int> dict(256, -1);        for (int i = 0; i != s.length(); ++i) {            //判断字符是否在start之后出现，出现过表示有重复字符，更新start            if (dict[s[i]] > start)                start = dict[s[i]];            //更新下标            dict[s[i]] = i;            //更新最大值            maxl = max(maxl, i-start);        }        return maxl;    }};