AoC Day 14 – Docking Data

This is a solution to Advent of Code 2020 day 14, written in Raku.

https://adventofcode.com/2020/day/14

Part One

Execute the initialization program. What is the sum of all values left in memory after it completes?

Raku

Raku's given / when construct is ideal for alternating input lines that require different parsing. I quickly realised that the mask could be applied to the values as a pair of and and or operations.

  my @lines = '14-input.txt'.IO.lines;

  my $and;
  my $or;

  my %mem;

  for @lines {
      when /'mask = ' (\w+)/ {
          my $mask = ~$0;
          $and = $mask.trans('X' => '1').parse-base(2);
          $or = $mask.trans('X' => '0').parse-base(2);
      }
      when /'mem[' (\d+) '] = ' (\d+)/ {
          %mem{~$0} = (+$1) +& $and +| $or;
      }
  }

  say [+] %mem.values;

15403588588538

Execute the initialization program using an emulator for a version 2 decoder chip. What is the sum of all values left in memory after it completes?

Raku

Part two is very similar, with the added step of generating all binary combinations for the sequence of X mask element then generating all the addresses to write into.

  my @lines = '14-input.txt'.IO.lines;

  my $or;
  my @bits;

  my %mem;

  sub base2-word($n, $width) {
      my $base2 = $n.base(2);
      '0' x ($width - $base2.chars) ~ $base2
  }

  for @lines {
      when /'mask = ' (\w+)/ {
          my $mask = ~$0;
          $or = $mask.trans('X' => '0').parse-base(2);

          my @mask = $mask.comb;
          @bits = (^@mask.elems).grep( -> $i { @mask[$i] eq 'X' });
      }
      when /'mem[' (\d+) '] = ' (\d+)/ {
          my $addr = base2-word((+$0) +| $or, 36);
          my $value = +$1;

          for ^(2 ** @bits.elems) -> $n {
              my $bit-values = base2-word($n, @bits.elems);
              my @addr = $addr.comb;
              @addr[@bits] = $bit-values.comb;
              %mem{@addr.join} = $value;
          }
      }
  }

  say "{+%mem} memory locations";
  say [+] %mem.values;

78824 memory locations
3260587250457

raku