Longest Substring Without Repeating Characters

题目

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.

分析

用start记录当前子串的开头，max记录到目前为止所出现的最长不重复子串的长度。

声明一个数组loca记录每个到目前为止每个字符出现的最后位置

遍历整个字符串，

若当前字符在当前子串中出现过，则将start赋值为当前字符出现的位置+1，

更新当前字符出现的位置，

如果当前子串的长度比max大，则更新max。

该算法复杂度为O（n)

代码

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