Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.

这里单纯的匹配还是可以实现的，但是时间复杂度有点高，我直接使用了简单哈希的方法，用了点空间换取时间，在一定程度上，空间占用的也不是很大。

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        char hash[128]={0};
        int start = 0,point = 0,lmax = 0;
        while(point<s.size())
        {
           hash[s[point]]>0?--hash[s[start++]]:++hash[s[point++]];
           lmax = max(lmax,point-start);
        }
        return lmax;
    }
};