Source: Corruption Checksum

Part 1: The checksum of a list of numbers is the difference between the largest and smallest number in the row. What is the sum of checksums of a file containing many such lists?

print(sum(
    max(*row) - min(*row)
    for row in data
))

It’s not the most Pythonic thing ever (closer to a lisp), but I think it’s still fairly clean. I think the most interesting part is using the * operator to send the entire list as parameters to max and min.

Part 2: Exactly two numbers in each list are evenly divisible by one another. The new checksum is the result of dividing the larger by the smaller. Find the sum of checksums.

This one looks similar, but instead of max and min, we’ll use % to check for divisibility and // to do integer division.

print(sum(
    a // b
    for row in data
    for a in row
    for b in row
    if a != b and a % b == 0
))

Really fast too:

$ python3 run-all.py day-02

day-02  python3 check-it.py input.txt --part 1  0.06736087799072266     51139
day-02  python3 check-it.py input.txt --part 2  0.0611109733581543      272