P4555 [CTT] Longest Double Palindromic Substring

A string that reads the same forward and backward is called a palindrome. For example, `acbca` is a palindrome, while `abc` is not: the forward order is `abc`, and the reverse is `cba`, which are not the same. Given a string $S$ of length $n$, find the longest double palindromic substring $T$ of $S$, that is, $T$ can be divided into two parts $X, Y$ (with $|X|, |Y| \ge 1$) and both $X$ and $Y$ are palindromes.

One line containing a string $S$ consisting of lowercase English letters.

One line with a single integer, the length of the longest double palindromic substring.

**Sample Explanation** Starting from the second character, the string `aacaabbacabb` can be split into two parts `aacaa` and `bbacabb`, and both are palindromes. **Constraints** For $100\%$ of the testdata, $2 \le |S| \le 10^5$. 2018.12.10, 2018.12.15: Thanks to @Ycrpro for providing two hack testdata sets. Translated by ChatGPT 5