Pascal triangle digit encryption

Digits are encrypted by folding them down an upside-down Pascal's triangle.

You get a list of n digits (each 0-9). In one round, replace the list with the sums of each pair of neighbours, keeping only the last digit of each sum ((a + b) % 10). The list gets one shorter each round. Stop when exactly two digits remain.

Implement:

def encrypt(digits: list[int]) -> str

Return the final two digits as a two-character string. Keep a leading zero ("07", not "7").

Constraints

• 2 <= n <= 1000 (a follow-up raises this to 10^5)
• every element is between 0 and 9

Example 1

digits = [1, 2, 3, 4]
round 1: [3, 5, 7]
round 2: [8, 2]
output: "82"

Example 2

digits = [0, 7]
already two digits
output: "07"