求字符串有多少个回文子串

 1 class Solution {
 2 public:
 3     int countSubstrings(string s) {
 4         int n = s.size(), sum = 0;
 5         for(int i = 0; i < n*2-1; i++)
 6         {
 7             int l = i / 2, r = i/2 + i%2;
 8             while(l>=0 && r < n && s[l] == s[r])
 9             {
10                 l--;
11                 r++;
12                 sum++;
13             }
14         }
15         return sum;
16     }
17 };