Manacher's Algorithm)

Returns the maximum length of the input substring.

 1 string longestPalindrome(string s) 2 { 3  4  5     int id, mx, i, j, len, maxlen; 6     vector<char> cvec; 7     vector<int> ivec; 8     string str; 9     int ma, k;10 11     id = 0;12     mx = 0;13     ivec.push_back(1);14     len = s.size();15     maxlen = 2*s.size() + 1;16 17     for (i = 0; i < len; ++i)18     {19         cvec.push_back(‘#‘);20         cvec.push_back(s[i]);21     }22     cvec.push_back(‘#‘);23 24 25     for (i = 1; i < maxlen; ++i)26     {27         if (mx > i)28         {29             int temp;30             temp = ((mx - i - 1) > (ivec[2*id - i])) ? (ivec[2*id - i]) : (mx - i - 1);31             ivec.push_back(temp);32         }33         else34             ivec.push_back(1); 35 36         for (; (i - ivec[i] >= 0) && ((i + ivec[i]) < maxlen) && (cvec[i-ivec[i]] == cvec[i+ivec[i]]); ++ivec[i])37             ;38 39         if (mx < ivec[i] + i -1 )40         {41             mx = ivec[i] + i - 1;42             id = i;43         }44     }45 46     ma = 0;47     for (i = 0; i < maxlen; ++i)48     {49         if (ivec[i] > ma)50         {51             ma = ivec[i];52             k = i;53         }54     }55 56     for (j = 0, i = k - ivec[k] + 1; j < ivec[k] - 1; ++i, ++j)57     {58         ++i;59         str.push_back(cvec[i]);60     }61     62     return str;63 }

 

Manacher's Algorithm)