AoC Day 12 – Rain Risk

This is a solution to Advent of Code 2020 day 12, written in Raku.

https://adventofcode.com/2020/day/12

Part One

Figure out where the navigation instructions lead. What is the Manhattan distance between that location and the ship's starting position?

Raku

This solution in Raku just uses an instruction loop to sequence through the input, maintaining position state along the way.

    my @instructions = '12-input.txt'.IO.lines;

    my %angle = E => 90, S => 180, W => 270, N => 0;
    my %point = 90 => 'E', 180 => 'S', 270 => 'W', 0 => 'N';

    my $dir = 'E';

    my ($x, $y) = 0, 0;

    for @instructions -> $instruction {
        my $action = $instruction.substr(0,1);
        my $value = +$instruction.substr(1);

        $action = $dir if $action eq 'F';

        given $action {
            when 'N' { $y += $value; }
            when 'S' { $y -= $value; }
            when 'E' { $x += $value; }
            when 'W' { $x -= $value; }
            when 'R' {
                my $new = (%angle{$dir} + $value) % 360;
                $dir = %point{$new};
            }
            when 'L' {
                my $new = (%angle{$dir} + 360 - $value) % 360;
                $dir = %point{$new};
            }
        }

        # say "{$action} {$value} -> {$x}, {$y}";
    }

    say "Manhattan distance: {abs($x) + abs($y)}";

Manhattan distance: 1589

Part Two

Figure out where the navigation instructions actually lead. What is the Manhattan distance between that location and the ship's starting position?

Raku

Part two is just a variation with some new state for maintaining the waypoint position.

  my @instructions = '12-input.txt'.IO.lines;
  #my @instructions = <F10 N3 F7 R90 F11>;

  my %angle = E => 90, S => 180, W => 270, N => 0;
  my %point = 90 => 'E', 180 => 'S', 270 => 'W', 0 => 'N';

  my ($x, $y) = 0, 0;
  my ($wx, $wy) = 10, 1;

  for @instructions -> $instruction {
      my $action = $instruction.substr(0,1);
      my $value = +$instruction.substr(1);

      given $action {
          when 'F' { for ^$value { $x += $wx; $y += $wy } }
          when 'N' { $wy += $value; }
          when 'S' { $wy -= $value; }
          when 'E' { $wx += $value; }
          when 'W' { $wx -= $value; }
          when 'R' {
              for ^($value div 90) {
                  my $tmp = $wy;
                  $wy = -$wx;
                  $wx = $tmp;
              }
          }
          when 'L' {
              for ^($value div 90) {
                  my $tmp = $wx;
                  $wx = -$wy;
                  $wy = $tmp;
              }
          }
      }

      # say "{$action} {$value} : waypoint {$wx}, {$wy} -> {$x}, {$y}";
  }

  say "Manhattan distance: {abs($x) + abs($y)}";

Manhattan distance: 23960

raku