最长不重复子串

 从头开始遍历字符串，对每一个遍历过的字符判断是否被标记过，若标记过，则更新左边界le=vis[temp]+1，同时更新当前不重复子串的长度；否则用数组下标进行标记，不断右移右边界ri，更新最大长度

class Solution
{
public:
    int lengthOfLongestSubstring(string s)
    {
        int le = 0, ri = 0, maxlen = 0, ans = 0;
        int len = s.length();
        int vis[256];
        for (int i = 0; i < 256; i++)
            vis[i] = -1;
        while(ri<len) {
            int temp = (char)s[ri];
            if (vis[temp] >=le) {
                le = vis[temp] + 1;
                maxlen = ri - le;
            }
            vis[temp] = ri;
            ri++;
            maxlen++;
            ans = max(ans, maxlen);
        }
        return ans;
    }
};