g1901_2000.s1930_unique_length_3_palindromic_subsequences

Class Solution

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 and Description
Solution()

Method Summary

Modifier and Type	Method and 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)