Package g2401_2500.s2484_count_palindromic_subsequences

Class Solution

  • All Implemented Interfaces:
    
public final class Solution

    2484 - Count Palindromic Subsequences\.

    Hard

    Given a string of digits s, return the number of palindromic subsequences of s having length 5. Since the answer may be very large, return it modulo <code>10<sup>9</sup> + 7</code>.

    Note:

    • A string is palindromic if it reads the same forward and backward.

    • A subsequence is a string that can be derived from another string by deleting some or no characters without changing the order of the remaining characters.

    Example 1:

    Input: s = "103301"

    Output: 2

    Explanation: There are 6 possible subsequences of length 5: "10330","10331","10301","10301","13301","03301". Two of them (both equal to "10301") are palindromic.

    Example 2:

    Input: s = "0000000"

    Output: 21

    Explanation: All 21 subsequences are "00000", which is palindromic.

    Example 3:

    Input: s = "9999900000"

    Output: 2

    Explanation: The only two palindromic subsequences are "99999" and "00000".

    Constraints:

    • <code>1 <= s.length <= 10<sup>4</sup></code>

    • s consists of digits.

    • 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 countPalindromes(String s)

      • Methods inherited from class java.lang.Object

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