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.

思路大概是建立一个映射表，遍历整个字符串，如果字符对应映射表的index值为-1，说明字符没出现过，计算长度大小，更新maxLength。如果字符出现过，那么就重新开始计算。遍历后得到最后结果。

class Solution {public:    int lengthOfLongestSubstring(string s) {        int indexOfChar[256];        memset(indexOfChar, -1, sizeof(indexOfChar));        int maxLength = 0;        int initIndex = -1;        for (int i = 0; i < s.length(); ++i){            if (indexOfChar[s[i]] > initIndex){                initIndex = indexOfChar[s[i]];            }            indexOfChar[s[i]]=i;            maxLength=max(maxLength, i - initIndex);        }        return maxLength;    }};

【LeetCode】3. Longest Substring Without Repeating Characters