Havannah = Hannah

Computer Science Level 5

Given a sequence of characters, you are asked to find the longest palindrome within it. There is a catch: the palindrome can be built by jumping over certain letters as long as it is in order. For example for the string havannah, the hiden palindrome would be:

\[\color{red} {\text{ha}} \text{va} \color{red} {\text{nnah}} = \text{hannah} \]

A string might have more than one such hidden palindrome. For example ,alfalfa has four hidden palindromes of length \(5\): 'alala', 'afafa', 'alfla','aflfa'

Find the length of the longest hidden palindrome for the following string.

Excel in math and science

Master concepts by solving fun, challenging problems.

It's hard to learn from lectures and videos

Learn more effectively through short, interactive explorations.

Used and loved by over 5 million people

Learn from a vibrant community of students and enthusiasts, including olympiad champions, researchers, and professionals.