Solution (leetcode-in-java 1.21 API)

java.lang.Object
- g0701_0800.s0730_count_different_palindromic_subsequences.Solution

```
public class Solution
extends Object
```
730 - Count Different Palindromic Subsequences.
Hard

Given a string s, return the number of different non-empty palindromic subsequences in s. Since the answer may be very large, return it modulo 10⁹ + 7.

A subsequence of a string is obtained by deleting zero or more characters from the string.

A sequence is palindromic if it is equal to the sequence reversed.

Two sequences a₁, a₂, … and b₁, b₂, … are different if there is some i for which a_i != b_i.

Example 1:

Input: s = “bccb”

Output: 6

Explanation: The 6 different non-empty palindromic subsequences are ‘b’, ‘c’, ‘bb’, ‘cc’, ‘bcb’, ‘bccb’. Note that ‘bcb’ is counted only once, even though it occurs twice.

Example 2:

Input: s = “abcdabcdabcdabcdabcdabcdabcdabcddcbadcbadcbadcbadcbadcbadcbadcba”

Output: 104860361

Explanation: There are 3104860382 different non-empty palindromic subsequences, which is 104860361 modulo 10⁹ + 7.

Constraints:
- 1 <= s.length <= 1000
- s[i] is either 'a', 'b', 'c', or 'd'.

- Constructor Summary
  
  Constructors
  Constructor Description
  
  Solution()
- Method Summary
  
  All Methods Instance Methods Concrete Methods
  Modifier and Type Method Description
  
  int countPalindromicSubsequences(String s)
  - Methods inherited from class java.lang.Object
    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail
- Solution
```
public Solution()
```

Method Detail

countPalindromicSubsequences

public int countPalindromicSubsequences(String s)