Student Attendance Record II

An attendance record for a student can be represented as a string where each character signifies whether the student was absent, late, or present on that day. The record only contains the following three characters:

  • 'A': Absent.
  • 'L': Late.
  • 'P': Present.

Any student is eligible for an attendance award if they meet both of the following criteria:

  • The student was absent ('A') for strictly fewer than 2 days total.
  • The student was never late ('L') for 3 or more consecutive days.

Given an integer n, return the number of possible attendance records of length n that make a student eligible for an attendance award. The answer may be very large, so return it modulo 10^9 + 7.

Example 1
Inputn = 2
Output8
There are 8 records with length 2 that are eligible for an award, and only "AA" is not eligible because there are 2 absences.
Example 2
Inputn = 1
Output3
The three records of length 1, "A", "L", and "P", are all eligible.

Constraints

  • 1 <= n <= 10^5

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