:tada:*Day 13 solution thread*:smiling_imp:

# advent-of-code

[bjonnh]

🎉*Day 13 solution thread*😈

[Marcin Wisniowski]

Part 1: https://gitlab.com/Nohus/advent-of-code-2020/-/blob/master/src/main/kotlin/day13_1/Solution.kt
Part 2: https://gitlab.com/Nohus/advent-of-code-2020/-/blob/master/src/main/kotlin/day13_2/Solution.kt

[bjonnh]

https://github.com/bjonnh/advent_of_code/blob/master/src/main/kotlin/y2020/day13/main.kt

[Jakub Gwóźdź]

probably should've used some smart modifications of lcm, but for giver input it still calculates in 6ms, so...

[ephemient]

https://github.com/ephemient/aoc2020/blob/main/kt/src/main/kotlin/io/github/ephemient/aoc2020/Day13.kt

[ephemient]

I originally implemented the direct computation of CRT: https://github.com/ephemient/aoc2020/blob/bda61d444c67dce6f0bfa69a54cf61974034b275/kt/src/main/kotlin/io/github/ephemient/aoc2020/math.kt

[ephemient]

but it requires BigInteger due to one of the last intermediate values being too large for a Long

[ephemient]

replacing it with the dumb sieve was faster

[Nir]

My solution exploits the fact that all the bus ID's are prime. I'm not crazy about that, although it is pretty simple/efficient as a result

[Nir]

Untitled

[Nir]

I think mine takes time proportional to the sum of the bus ID's, which is pretty good

[todd.ginsberg]

Ended up with this, which looks similar to some others here...

Blog: https://todd.ginsberg.com/post/advent-of-code/2020/day13/

Code: https://github.com/tginsberg/advent-2020-kotlin/blob/main/src/main/kotlin/com/ginsberg/advent2020/Day13.kt