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 <= 1000s consists of lowercase English letters.