647. Palindromic Substrings

Posted 2020-10-17 jxr041100

Given a string, your task is to count how many palindromic substrings in this string.

The substrings with different start indexes or end indexes are counted as different substrings even they consist of same characters. 

Example 1:

Input: "abc"
Output: 3
Explanation: Three palindromic strings: "a", "b", "c".

 

Example 2:

Input: "aaa"
Output: 6
Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".

class Solution {
public:
    int countSubstrings(string s) {
        int cnt = 0;
        int n = s.size();
        for(int i = 0;i<s.size();i++)
        {
            cnt +=count_palindromic(s,i,i);
            cnt += count_palindromic(s,i,i+1);
        }
        return cnt;
    }
private:
    int count_palindromic(string s,int left,int right)
    {
        int cnt = 0;
        while(left>=0&&right<s.size())
        {
            if(s[left]==s[right])
            {
                cnt++;
                left--;
                right++;
            }
            else
                break;
        }
        return cnt;
    }
};