Day 17: A-star using Array::Heap

[aoc.git] / 2023 / 33.pl

diff --git a/2023/33.pl b/2023/33.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 + $ymax, 0, 0, 0, 0, 0, [0, 0] ];
+my %min_cost;
+$min_cost{0,0,0,0} = 0; # $x, $y, $dir, $dist
+
+while (@q) {
+       my $node = pop_heap @q;
+       my ($w, $x, $y, $cost, $prevdir, $dist, @path) = @$node;
+
+       if ($x == $xmax && $y == $ymax) {
+               say "$cost : ", join(', ', map { join(',', @$_) } @path);
+               last;
+       }
+
+       for my $dir (0 .. 3) {
+               next if $dir == ($prevdir ^ 2);
+
+               my $nx = $x + $dx[$dir];
+               my $ny = $y + $dy[$dir];
+               next if $nx > $xmax || $ny > $ymax || $nx < 0 || $ny < 0;
+
+               my $ndist = ($dir == $prevdir) ? $dist+1 : 1;
+               next if $ndist > 3;
+
+               my $ncost = $cost + $map[$ny][$nx];
+               next if defined $min_cost{$nx,$ny,$dir,$ndist}
+                       && $min_cost{$nx,$ny,$dir,$ndist} <= $ncost;
+               $min_cost{$nx,$ny,$dir,$ndist} = $ncost;
+               my $nw = ($xmax-$nx) + ($ymax-$ny) + $ncost;
+               push_heap @q, [ $nw, $nx, $ny, $ncost, $dir, $ndist, @path, [$nx, $ny] ];
+       }
+}
+