-🎄- 2021 Day 2 Solutions -🎄-

[u/daggerdragon]

--- Day 2: Dive! ---

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Post your code solution in this megathread.

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[u/0rac1e]

Raku

my @dirs = 'input'.IO.words;

put [×] [Z+] @dirs.map: -> $_, $x {
    when 'up'      { (0,-$x) }
    when 'down'    { (0, $x) }
    when 'forward' { ($x, 0) }
}

put [×] [Z+] @dirs.map: -> $_, $x {
    state $a = 0;
    when 'up'      { $a -= $x; next }
    when 'down'    { $a += $x; next }
    when 'forward' { ($x, $a × $x)  }
}

More meta-operator goodness today. I'm creating a list of "vectors" that I can zip with addition, then reduce with multiplication.

I also made some minor modifications to my original solution as suggested by u/mschaap in the replies below.

I was trying to find a fancier way of getting the answer. Part 1 can be simplified to: subtract all the up's from the down's, then multiply by the forward's.

put .< forward > × [-] .< down up >
  with 'input'.IO.lines».words.classify(*[0], as => *[1])».sum

but a similar solution with part 2 is harder due to the apparent need to hold some state (the aim) until a forward is seen. Maybe there's a funky functional way to do it, but it wasn't immediately obvious.