Package g0701_0800.s0730_count_different_palindromic_subsequences

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    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 <code>10<sup>9</sup> + 7</code>.

    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 <code>a<sub>1</sub>, a<sub>2</sub>, ...</code> and <code>b<sub>1</sub>, b<sub>2</sub>, ...</code> are different if there is some i for which <code>a<sub>i</sub> != b<sub>i</sub></code>.

    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 10<sup>9</sup> + 7.

    Constraints:

    • 1 &lt;= s.length &lt;= 1000

    • s[i] is either 'a', 'b', 'c', or 'd'.

    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description

    • Field Summary

      Fields 
      Modifier and Type Field Description

    • Constructor Summary

      Constructors 
      Constructor Description
      Solution()

    • Enum Constant Summary

      Enum Constants 
      Enum Constant Description

    • Method Summary

      Modifier and Type Method Description
      final Integer countPalindromicSubsequences(String s)

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait