https://leetcode.com/problems/longest-palindromic-substring/

Expand from center, check for even and odd palindromes

class Solution {
public:
  string longestPalindrome(string s) {
    if (s.size() < 1)
      return "";
    int start = 0;
    int l = s.size();
    int maxLength = 1;

    for (int i = 0; i < l; i++) {
      // Odd
      int low = i - 1, high = i;
      while (low >= 0 && high < l && s[low] == s[high]) {
        if (high - low + 1 > maxLength) {
          start = low;
          maxLength = high - low + 1;
        }
        low--;
        high++;
      }
      // Even
      low = i - 1, high = i + 1;
      while (low >= 0 && high < l && s[low] == s[high]) {
        if (high - low + 1 > maxLength) {
          start = low;
          maxLength = high - low + 1;
        }
        low--;
        high++;
      }
    }
    return s.substr(start, maxLength);
  }
};