Day 17: A-star using Array::Heap

[aoc.git] / 2023 / 34.pl

diff --git a/2023/34.pl b/2023/34.pl
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+#!/usr/bin/perl -w
+
+use v5.38;
+use experimental 'multidimensional';
+use Array::Heap;
+$; = ';';
+
+my @map = map { chomp; [ split // ] } <>;
+my $xmax = $#{ $map[0] };
+my $ymax = $#map;
+
+my @dx = (1, 0, -1, 0);
+my @dy = (0, 1, 0, -1);
+
+my @q;
+push_heap @q, [ $xmax + $ymax, 0, 0, 0, 4, [0, 0] ];
+my %min_cost;
+$min_cost{0,0,0} = 0; # $x, $y, $dir
+while (@q) {
+       my $node = pop_heap @q;
+       my ($w, $x, $y, $cost, $prevdir, @path) = @$node;
+
+       if ($x == $xmax && $y == $ymax) {
+               say "$cost : ", join(', ', map { join(',', @$_) } @path);
+               last;
+       }
+
+       DIR:
+       for my $dir (0 .. 3) {
+               next if $dir == ($prevdir ^ 2) || $dir == $prevdir;
+               my $nx = $x;
+               my $ny = $y;
+               my $ncost = $cost;
+               for (1 .. 10) {
+                       $nx += $dx[$dir];
+                       $ny += $dy[$dir];
+                       next DIR if $nx > $xmax || $ny > $ymax || $nx < 0 || $ny < 0;
+                       $ncost += $map[$ny][$nx];
+                       next if $_ < 4;
+                       next if defined $min_cost{$nx,$ny,$dir}
+                               && $min_cost{$nx,$ny,$dir} <= $ncost;
+                       $min_cost{$nx,$ny,$dir} = $ncost;
+                       my $nw = ($xmax-$nx) + ($ymax-$ny) + $ncost;
+                       push_heap @q, [ $nw, $nx, $ny, $ncost, $dir, @path, [$nx, $ny] ];
+               }
+       }
+}
+