class Solution { public: string longestPalindrome(string s) { if (s.length() == 0) return ""; int len = s.length(); int f[len][len]; memset(f, 0, sizeof(f)); int ans = 1; int start = 0; for (int i = 0; i < len; i++) { f[i][i] = 1; for (int j = 0; j < i; j++) { if (s[j] == s[i] && (i - j < 2 || f[j+1][i⑴])) f[j][i] = 1; if (f[j][i] && i - j + 1 > ans){ ans = i - j + 1; start = j; } } } return s.substr(start, ans); } };