Today's puzzle made me come up with a monster: `in...

# advent-of-code

[Leon Linhart]

Today's puzzle made me come up with a monster: intersectAllBy

https://github.com/TheMrMilchmann/AdventOfCode2019/blob/f42664c0330b1ba9010c6aac498d79d4fb094489/src/main/kotlin/day03/part2/main.kt#L67

[Kroppeb]

I don't understand what it's doing

[Leon Linhart]

It basically calculates the intersection of an arbitrary number of sets based on part of their elements. (Well that doesn't make it any better, does it? Here, an example using simple math terms:)

Let X = {(A, 1), (A, 2), (B, 1)}
and Y = {(A, 3), (B, 5), (C, 2)}

Here, obviously no two elements of X and Y are equal and thus the intersection is empty, but X.intersectBy(Y) { it.LETTER } would yield {(A, 1), (A, 2), (A, 3), (B, 1), (B, 5)} .

At first I thought the second part would require us to deal with more than two wires so I wrote intersectAll and intersectAllBy to calculate the intersection of an abritrary sequence of sets.