Palindromic Substring

Problem Statement

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.

Leetcode link

Examples

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.

Code

Python3 Code

class Solution:
    def countSubstrings(self, s: str) -> int:
        res = n = len(s)
        for i in range(n):
            r = l = i
            while r + 1 < n and s[l] == s[r+1]:
                r += 1
                res += 1
            while r + 1 < n and l > 0 and s[l-1] == s[r+1]:
                r += 1
                l -= 1
                res += 1
        return res