longest_palindrome.cpp

#include <vector>
#include <algorithm>
#include <string_view>

class Solution {
public:
    string longestPalindrome(string s) {
        std::size_t s_length{ s.length() };
        string longest_palindrome;
        
        // i == start index, j == end index
        for (std::size_t i{}; i <= s_length; ++i)
        {
            for (std::size_t j{i}; j <= s_length; ++j)
            {
                string_view s_view{s};
                string_view substr_view{s_view.substr(i, j - i)};
                if (substr_view.length() >= 2 && std::equal(substr_view.begin(), substr_view.end(), substr_view.rbegin()))
                {
                    if (static_cast<int>(substr_view.length()) > longest_palindrome.length())
                    {
                        longest_palindrome = substr_view;
                    }
                }
            }
        }
        
        if (longest_palindrome == "")
        {
            string str{s[0]};
            longest_palindrome = str;
        }
        
        return longest_palindrome;
    }
};