Attendance register

Find the students whose term attendance has fallen below a threshold.

A register is a string "Name:CODES". CODES has one character per class session, in order:

• P present: the student attended.
• L late: the student attended, except that every third late of the term (the 3rd, 6th, 9th, ...) counts as an absence instead.
• A absent: the student did not attend.
• E excused: the session is skipped entirely and counts neither for nor against the student.

Sessions that count are all sessions except the E ones. A student's attendance percentage is attended * 100 // counted (rounded down). If no sessions count (no sessions yet, or all excused), the percentage is 100.

Return every student whose percentage is strictly below threshold.

Input: registers, a list of strings in the format above, and threshold, an integer.

Output: a list of [name, percentage] pairs, ordered by percentage ascending, then by name in plain alphabetical (code point) order.