Leetcode 647. Palindromic Substrings. Python (O(n^2))

647. Palindromic Substrings 

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.

Solution :

class Solution:
    def countSubstrings(self, s: str) -> int:
        ans = 0
        
        for i in range(len(s)):
            ans += self.pcount(s, i, i)
            ans += self.pcount(s, i, i+1)

        return ans
    
    def pcount(self, s, l, r):
        ans = 0
        while l >= 0 and r < len(s) and s[l] == s[r]:
            ans += 1
            l -= 1
            r += 1
        return ans

Explanation :