Leetcode647-palindromicSubstrings

Description

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

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:

1. The input string length won’t exceed 1000.

Solution

class Solution {
    public int extendPalind(String s, int left, int right){
        int count = 0;
        while (left >= 0 && right < s.length() && s.charAt(left) == s.charAt(right)){
            count ++;
            left --;
            right ++;
        }
        return count;
    }
    
    public int countSubstrings(String s) {
        if (s == null || s.length() == 0) return 0;
        int res = 0;
        for (int i = 0; i < s.length(); i++){
            res += extendPalind(s, i, i);
            res += extendPalind(s, i, i+1);
        }
        return res;
    }
}

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