# 647. Palindromic-Substrings

difficulty: Medium

&#x20;section pre{ background-color: #eee; border: 1px solid #ddd; padding:10px; border-radius: 5px; }&#x20;

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:**

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

## Method One

```java
class Solution {
    public int countSubstrings(String s) {
        // 和 005 一样，没啥意思
        int total = 0;
        for(int i = 0; i < s.length(); i++ ) {
            total += expand(s, i, i);
            total += expand(s, i, i + 1);
        }
        return total;
    }
    public int expand(String s, int i, int j) {
        int count = 0;
        while( i >= 0 && j < s.length() ){
            if( s.charAt(i) == s.charAt(j) ) {
                i--;
                j++;
                count++;
            }else{
                return count;
            }
        }
        return count;
    }
}
​
```
