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".

Solution: 以每个字母为中心扩展找palindrom(奇偶两种情况)

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