LeetCode: 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 asubstring,"pwke" is a subsequence and not a substring.

给定一个字符串，要求给出其最长无重复字符的子串的长度

给出"abcabcbb", 符合要求的子串是 "abc", 长度是3.

给出 "bbbbb", 符合要求的子串是"b", 长度是1.

给出 "pwwkew",符合要求的子串是"wke", 长度是3. 注意答案要求的是子串, "pwke" 是一个子字符序列而并非子串.

思路：

假设有字符串a0,a1,a2,...,an,要求得他的最长无重复子串可以从a0开始，若a0,a1,...,ai 各不相同，那a0到ai的最长无重复子串就是他自己,我们把他的长度做一个备份s0，假定ai+1等于a0到ai中的一个元素aj，显然包含ai+1的最长无重复子串为aj+1,...,ai+1.故我们以aj+1为无重复子串的左端点继续向右，直到遍历整个字符串之后s0,s1,s2,...,sk,..中最大的值即为最长无重复字符的子串的长度。

代码

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