PalindromicSubstrings.java

/*
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".
*/
class Solution {
    public int countSubstrings(String s) {
        if(s.length() == 1) return 1;
        int count_subs = 0;
        for(int i = 0;i < s.length(); i++){
            //counting odd length substrings
            count_subs += substr(s, i, i);
            

            //counting even length substrings
            count_subs += substr(s, i, i+1);
        }
        return count_subs;
    }

    private int substr(String s, int left, int right){
        int count = 0;
        while(left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)){
            left--;right++;count++;
        }
        return count;
    }
}