Palindromic Substrings

Palindromic Substrings dynamic programming

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".
Note:
The input string length won't exceed 1000.

Palindromic Substrings Solution

class PalindromicSubstrings {
    int result = 0;
    public int countSubstrings(String s) {
        if(s == null || s.length() == 0) {
            return 0;
        }

        for(int i = 0; i < s.length(); i++) {
            extendPalindrome(s, i, i);
            extendPalindrome(s, i, i + 1);
        }

        return result;
    }

    public void extendPalindrome(String s, int left, int right) {
        while(left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)) {
            result++;
            left--;
            right++;
        }
    }
}

Last modified October 4, 2020