AoC 2022, day 12

my ($rows, $cols);

sub solve(@M, Complex:D $start, Complex:D $target --> UInt:D) {
    my %dists = $start => 0.Int;
    my @Q = $start;

    while @Q {
        my @Q_;

        for @Q -> $p {
            my $elevation = @M[$p.re;$p.im];
            my $dist = %dists{$p};

            for (-i, i, -1.Complex, 1.Complex) -> $move {
                my $p_ = $p + $move;
                next unless 0 ≤ $p_.re ≤ $rows - 1;
                next unless 0 ≤ $p_.im ≤ $cols - 1;

                my $elevation_ = @M[$p_.re;$p_.im];
                next unless ord($elevation_) - ord($elevation) ≤ 1;

                without %dists{$p_} {
                    %dists{$p_} = $dist + 1;
                    return($dist + 1) if $p_ == $target;
                    @Q_.push($p_);
                }
            }
        }

        @Q = @Q_;
    }

    $rows * $cols       # ∞
}

my @M = $*IN.lines.map({ .comb.Array }).Array;
$rows = +@M;
$cols = +@M[0];

my $start  = do with @M[*;*].first('S', :k) { ($_ div $cols + ($_ mod $cols)i).Complex };
@M[$start.re;$start.im] = 'a';
my $target = do with @M[*;*].first('E', :k) { ($_ div $cols + ($_ mod $cols)i).Complex };
@M[$target.re;$target.im] = 'z';

put 'part 1: ', solve(@M, $start, $target);

put 'part 2: ', do for @M[*;*].grep('a', :k) -> \ndx {
    solve(@M, (ndx div $cols + (ndx mod $cols)i).Complex, $target)
}.min;