Palindromic Substrings

Count all palindromic contiguous substrings of s. Substrings with identical text at different positions count separately, and every single character is a palindrome.

Input / output

• Input: s: string
• Output: integer count

Examples

1. "abc" returns 3.
2. "aaa" returns 6: three single characters, two "aa" substrings, and one "aaa".

Constraints

• 1 <= s.length <= 1,000
• s contains lowercase English letters.

Follow-up Explain why expanding around 2n - 1 centers is quadratic time but constant extra space.