INCLAW
The AI That Thinks, Codes, Conquers.

1def longest_palindrome(s: str) -> str:
2    """Find the longest palindromic substring using expand-around-center."""
3    if len(s) < 2:
4        return s
5    
6    start, max_len = 0, 1
7    
8    def expand(left: int, right: int) -> None:
9        nonlocal start, max_len
10        while left >= 0 and right < len(s) and s[left] == s[right]:
11            if right - left + 1 > max_len:
12                start = left
13                max_len = right - left + 1
14            left -= 1
15            right += 1
16    
17    for i in range(len(s)):
18        expand(i, i)      # Odd length palindromes
19        expand(i, i + 1)  # Even length palindromes
20    
21    return s[start:start + max_len]
22
23# Example usage
24print(longest_palindrome("babad"))  # Output: "bab"
25print(longest_palindrome("cbbd"))   # Output: "bb"