[leetcode]第3题

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