LeetCode "Longest Palindromic Substring" revisited

class Solution {
public:
    string longestPalindrome(string s) 
    {    
        size_t slen = s.length();
        if (slen < 2) return s;

        //    inserting tokens to original string
        string ns = "#";
        for (auto c : s)
        {
            ns += c;
            ns += "#";
        }

        //
        size_t len = ns.length();
        vector<size_t> rec(len, 0);

        int maxi = 1, maxr = 0;
        int ci = 1, r = 0;
        for (size_t i = 1; i < len; i++)
        {            
            int myr = 0;        //    brand new index
            if (i <= (ci + r))    //    can be reused due to symmetry
            {                
                myr = std::min(rec[2 * ci - i], (ci + r) - i);
            }
            //    expand to new inx towards end of string
            bool bMis = false;
            int max_ex = std::min(len - 1 - i, i);
            while (myr < max_ex)
            {
                myr++;
                if (ns[i + myr] != ns[i - myr])
                {
                    bMis = true;
                    break;
                }
            }
            if (bMis) myr--;
            
            //    book-keeping
            rec[i] = myr;
            if ((i + myr) > (maxi + maxr))
                ci = i, r = myr;

            if (myr > maxr)    //     record max
            {
                maxi = i, maxr = myr;
            }
        }

        string raw = ns.substr(maxi - maxr, maxr * 2 + 1);
        string ret;
        for (auto c : raw)
        {
            if (c != '#') ret += c;
        }
        return ret;
    }
};