days 5-11

7/1.pl

@@ -0,0 +1,66 @@
+#!/usr/bin/perl
+
+use strict;
+use v5.10;
+use Data::Dumper;
+
+chomp (my @data = <STDIN>);
+
+my %deps;
+my %steps;
+foreach my $line (sort @data) {
+    my ($dep, $step) = ($line =~ /Step (\S+) must be finished before step (\S+) can begin\./);
+    say "$dep, $step";
+    if (exists $deps{$step}) {
+        my $t =  $deps{$step};
+        push @$t, $dep;
+        $deps{$step} = $t;
+    } else {
+        my @add = ($dep);
+        $deps{$step} = \@add;
+    }
+    $steps{$dep}=0;
+    $steps{$step}=0;
+}
+
+my @final;
+while (my @doable = find_nextsteps(\%deps) )  {
+    my $first = $doable[0];
+    mark_complete($first, \%deps);
+    push @final, $first;
+}
+
+say join "", @final;
+
+
+sub mark_complete {
+    my ($step, $deps) = @_;
+
+    # complete task.
+    $steps{$step} = 1;
+    # remove from dep list.
+    foreach my $s (sort keys %$deps) {
+        my @tasks = @{$$deps{$s}};
+        @tasks = grep {!/$step/} @tasks;
+        if ($#tasks > -1) {
+            $$deps{$s} = \@tasks;
+        } else {
+            delete $$deps{$s};
+        }
+    }
+}
+
+sub find_nextsteps {
+    my ($deps) = @_;
+
+    # find next.
+    my @doable;
+    foreach my $s (sort keys %steps) {
+        next if ($steps{$s} == 1);
+        if (!$$deps{$s}) {
+            push @doable, $s;
+        }
+    }
+
+    return sort @doable;
+}