0552. Student Attendance Record II

https://leetcode.com/problems/student-attendance-record-ii

Description

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 109 + 7.

Example 1:

**Input:** n = 2
**Output:** 8
**Explanation:** There are 8 records with length 2 that are eligible for an award:
"PP", "AP", "PA", "LP", "PL", "AL", "LA", "LL"
Only "AA" is not eligible because there are 2 absences (there need to be fewer than 2).

Example 2:

**Input:** n = 1
**Output:** 3

Example 3:

**Input:** n = 10101
**Output:** 183236316

Constraints:

• 1 <= n <= 105

ac