Solution (leetcode-in-java 1.24 API)

java.lang.Object
- g1901_2000.s1930_unique_length_3_palindromic_subsequences.Solution

```
public class Solution
extends Object
```
1930 - Unique Length-3 Palindromic Subsequences.
Medium

Given a string s, return the number of unique palindromes of length three that are a subsequence of s.

Note that even if there are multiple ways to obtain the same subsequence, it is still only counted once.

A palindrome is a string that reads the same forwards and backwards.

A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.
- For example, "ace" is a subsequence of "abcde".
Example 1:

Input: s = “aabca”

Output: 3

Explanation: The 3 palindromic subsequences of length 3 are:
- “aba” (subsequence of “aabca”)
- “aaa” (subsequence of “aabca”)
- “aca” (subsequence of “aabca”)
Example 2:

Input: s = “adc”

Output: 0

Explanation: There are no palindromic subsequences of length 3 in “adc”.

Example 3:

Input: s = “bbcbaba”

Output: 4

Explanation: The 4 palindromic subsequences of length 3 are:
- “bbb” (subsequence of “bbcbaba”)
- “bcb” (subsequence of “bbcbaba”)
- “bab” (subsequence of “bbcbaba”)
- “aba” (subsequence of “bbcbaba”)
Constraints:
- 3 <= s.length <= 10⁵
- s consists of only lowercase English letters.

- Constructor Summary
  
  Constructors
  Constructor Description
  
  Solution()
- Method Summary
  
  All Methods Instance Methods Concrete Methods
  Modifier and Type Method Description
  
  int countPalindromicSubsequence(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

countPalindromicSubsequence

public int countPalindromicSubsequence(String s)