Student Attendance Record II Python Solution

lcpy gen -n 552   # by problem number
lcpy gen -s student_attendance_record_ii   # by problem name

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).

Input: n = 1
Output: 3

Input: n = 10101
Output: 183236316

class Solution:
    # Time: O(n)
    # Space: O(1)
    def check_record(self, n: int) -> int:
        mod = 1_000_000_007
        # dp[a][l]: records ending with `a` total absences and `l` trailing
        # consecutive lates.
        dp = [[0] * 3 for _ in range(2)]
        dp[0][0] = 1
        for _ in range(n):
            no_absent = sum(dp[0]) % mod
            with_absent = sum(dp[1]) % mod
            nxt = [
                # append 'P' (late streak resets); 'A' starts the streak anew
                [no_absent, dp[0][0], dp[0][1]],
                [(no_absent + with_absent) % mod, dp[1][0], dp[1][1]],
            ]
            dp = nxt
        return (sum(dp[0]) + sum(dp[1])) % mod