Leetcode 5. Longest Palindromic Substring 题解

class Solution {
    public:
        std::string longestPalindrome(std::string s) {
            if (s.size()==0)
                return s;
            size_t max_len = 0;
            std::pair<size_t, size_t> res_ij;
            for (size_t i = 0; i < s.size(); ++i)
            {
                // odd case
                for (size_t j = 1; j <= i && i + j < s.size(); ++j)
                {
                    if (s[i - j] == s[i + j])
                    {
                        if (2 * j + 1 > max_len)
                        {
                            max_len = 2 * j + 1;
                            res_ij = std::make_pair(i, j);
                        }
                    }
                    else
                    {
                        break;
                    }
                }

                // even case
                for (size_t j = 1; j <= i && i + j -1 < s.size(); ++j)
                {
                    if (s[i - j] == s[i + j -1])
                    {
                        if (2 * j > max_len)
                        {
                            max_len = 2 * j;
                            res_ij = std::make_pair(i, j);
                        }
                    }
                    else
                    {
                        break;
                    }
                }
            }
            return max_len != 0 ? s.substr(res_ij.first - res_ij.second, max_len):s.substr(0, 1);
        }
};