Count Palindromic Subsequences
Given a string of digits s, return the number of palindromic subsequences of s having length 5.
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 10^9 + 7.
Note:
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 <= 10^4
- s consists of digits.
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