Class Solution
java.lang.Object
g2401_2500.s2484_count_palindromic_subsequences.Solution
public class Solution
extends java.lang.Object
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 109 + 7
.
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:
1 <= s.length <= 104
s
consists of digits.
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Constructor Summary
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Method Summary
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
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Constructor Details
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Solution
public Solution()
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Method Details
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countPalindromes
public int countPalindromes(java.lang.String s)
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