647.回文子串

class Solution:
    def countSubstrings(self, s: str) -> int:
        res=0
        for i in range(len(s)):
            # aba 
            left ,right =i,i 
            while left >=0 and right< len(s) and s[left] == s[right]:
                res +=1
                left -=1
                right +=1
            #abba 
            left =i 
            right= i+1
            while left >=0 and right< len(s) and s[left] == s[right]:
                res +=1
                left -=1
                right +=1
        return res