Palindromic Substrings

 This Article is for self practice

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.

package practice;

public class PalindromicString {

    public static void main(String[] args) {

        /*

        Input: s = "aaa"
    Output: 6
        Explanation: Six palindromic strings: "a", "a", "a", "aa", "aa", "aaa".
        * */

        PalindromicString ps = new PalindromicString();

        String s = "aaa";

        System.out.println(ps.countSubstrings(s));

    }


    public int countSubstrings(String s) {
        int ans = 0;

        for (int i = 0; i < s.length(); i++) {

            //odd digit palindrome
            ans = ans + findPalindrome(s, i, i);

            //even digit palindtrome
            ans = ans + findPalindrome(s, i, i + 1);
        }

        return ans;
    }


    int findPalindrome(String s, int l, int h) {
        int ans = 0;
        while (l >= 0 && h < s.length()) {
            if (s.charAt(l) != s.charAt(h)) {
                break;
            }
            l--;
            h++;
            ans++;
        }
        return ans;
    }
}