647\. Palindromic Substrings

Medium

Given a string `s`, return _the number of **palindromic substrings** in it_.

A string is a **palindrome** when it reads the same backward as forward.

A **substring** is a contiguous sequence of characters within the string.

**Example 1:**

**Input:** s = "abc"

**Output:** 3

**Explanation:** Three palindromic strings: "a", "b", "c". 

**Example 2:**

**Input:** s = "aaa"

**Output:** 6

**Explanation:** Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa". 

**Constraints:**

*   `1 <= s.length <= 1000`
*   `s` consists of lowercase English letters.