StaffDynamic Programming
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
Input
n = 2Output
8There 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
Input
n = 1Output
3The three records of length 1, "A", "L", and "P", are all eligible.
Constraints
- 1 <= n <= 10^5