c_cpp 给定一个字符串S，找到S中最长的回文子字符串。您可以假设S的最大长度为1000，并且存在一个单一的

Posted 2021-05-14

string longest_palindrome(const string& s) {
    if(s.empty()) return "";
    int N = s.size();
    int max_len = 1, start = 0;  // gist, start should be initialized. otherwise, "a" will have error
    for(int i=0; i<N; ++i) {    // should be N not N-1
        int j = i, k = i;
        while(j >= 0 && k < N) {
            if(s[j] != s[k]) break;
            if(max_len < k-j+1) {
                max_len = k-j+1;
                start = j;
            }
            j--;
            k++;
        }
        j = i; k = i+1;
        while(j >= 0 && k < N) {
            if(s[j] != s[k]) break;
            if(max_len < k-j+1) {
                max_len = k-j+1;
                start = j;
            }
            j--;
            k++;
        }
    }
    return s.substr(start, max_len);
}