Package g0701_0800.s0730_count_different_palindromic_subsequences

Class Solution

java.lang.Object
g0701_0800.s0730_count_different_palindromic_subsequences.Solution
public class Solution extends java.lang.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 ai != bi.

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

    Modifier and Type
    Method
    Description
    int
    countPalindromicSubsequences(java.lang.String s)
     

    Methods inherited from class java.lang.Object

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

  • Constructor Details

    • Solution

      public Solution()

  • Method Details

    • countPalindromicSubsequences

      public int countPalindromicSubsequences(java.lang.String s)