输入：“pwwkew”

输出：“3”

过程：求最长不重复字符子串长度

• 简单暴力求解：
  代码如下：

int lengthOfLongestSubstring(string s)
{
    string subStr = "";
    int maxlen = 0;
    for (int i = 0; i < s.length(); i++)
    {
        size_t found = subStr.find(s[i]);
        if (subStr.find(s[i]) != string::npos) // found
        {
            subStr = subStr.substr(found+1);
        }
        subStr.push_back(s[i]);

        maxlen = (maxlen < subStr.length()) ? subStr.length() : maxlen;
    }
    return maxlen;
}

• 字符映射

int lengthOfLongestSubstring_star(string s) {
    int start = 0;
    int maxlen = 1;

    if (s.size() == 0)
        return 0;

    vector<int> location(128, -1);//ascii 128 bit

    for (int i = 0; i<s.length(); i++)
    {
        if (location[s[i]] >= start)
        {
            start = location[s[i]] + 1;
        }

        location[s[i]] = i;

        int strlen = i - start + 1;
        maxlen = max(maxlen, strlen);
    }

    return maxlen;
}