aoc2021

day04-1.pl (4669B) - raw

---

 #!/usr/bin/env perl
 
 use strict;
 use warnings;
 use v5.22;
 
 sub get_filehandle {
     if (@ARGV !=1) {
         die "Usage: $0 [input-filename]";
     }
     my $input_filename = $ARGV[0];
     open my $filehandle, '<', $input_filename or
         die "Could not open input file $input_filename: $!";
     return $filehandle;
 }
 
 sub get_numbers {
     my $fh = shift;
     chomp( my $numbers = ( <$fh> ) );
     return (split( ",", $numbers));
 }
 
 sub initialize_boards {
     my $fh = shift;
     chomp( my @input = ( <$fh> ) );
     my (@boards, @new_board);
     foreach (@input) {
         if (/\A\s*\Z/) {
             push(@boards, [@new_board]) if (@new_board);
             @new_board = ();
         } else {
             push(@new_board, [split]);
         }
     }
     push(@boards, \@new_board);
     return (@boards);
 }
 
 sub initialize_state {
     my %state;
     my $boards = shift;
     foreach my $board (@$boards) {
         foreach my $row (@$board) {
             foreach my $column (@$row) {
                 $state{$board}{$row}{$column} = 0;
             }
         }
     }
     return %state;
 }
 
 sub play_turn {
     my ($number, $boards, $state) = @_;
     printf "playing number %2d\n", $number;
     foreach my $board (@$boards) {       # $board is ref to board array
         foreach my $row (@$board) {      # $row is ref to board row array
             foreach my $column (@$row) { # $column is element of row array
                 if ($column == $number) {
                     $state->{$board}{$row}{$column} = 1;
                 }
             }
         }
     }
 }
 
 # for debugging purposes only
 sub print_board_state {
     my ($boards, $state) = @_;
     foreach my $board (@$boards) {       # $board is ref to board array
         foreach my $row (@$board) {      # $row is ref to board row array
             foreach my $column (@$row) { # $column is element of row array
                 print "$board\t$row\t";
                 if ($state->{$board}{$row}{$column} == 1) {
                     printf "-> %2d <-\n", $column;
                 } else {
                     printf "   %2d\n", $column;
                 }
             }
         }
     }
 }
 
 sub check_for_winner {
     my ($boards, $state) = @_;
 # check for row wins
     foreach my $board (@$boards) {       # $board is ref to board array
         foreach my $row (@$board) {      # $row is ref to board row array
             my $total = 0;
             foreach my $column (@$row) { # $column is the actual value of
                                          # the number in @$row
                 $total += $state->{$board}{$row}{$column};
             }
             if ($total == 5) {
                 #say "found row winner";
                 return $board;
             }
         }
 # for each board, iterate through each column (0 .. 4)
         foreach (0 .. 4) {
             my $total = 0;
             foreach my $row (@$board) {
 # here, $_ represents the index within the array @$row.  Because the hash key
 # stores the actual value, we need to deference $row (which is an array
 # reference) and then look up the value stored in the index $_
                 $total += $state->{$board}{$row}{$row->[$_]};
             }
             if ($total == 5) {
                 #say "found column winner";
                 return $board;
             }
         }
     }
     return 0; # no winner found
 }
 
 sub calculate_score {
     my ($number, $board, $state) = @_;
     my $score = 0;
     foreach my $row (@$board) {     # $row is ref to board row array
         foreach my $column (@$row) { # $column is element of row array
             if ($state->{$board}{$row}{$column} == 0) {
                 $score += $column;
             }
         }
     }
     return $score *= $number;
 }
 
 # Advent of Code 2021 Day 04 Part 1
 # initialize game variables
 my $filehandle  = get_filehandle();
 my @numbers     = get_numbers($filehandle);
 my $number;
 my @boards      = initialize_boards($filehandle);
 my %state       = initialize_state(\@boards);
 my $turn = 0;
 
 # $winner_found plays double duty.  When equal to 0, it means that
 # we haven't yet found a winning board.  When we do, the subroutine
 # check_for_winner returns a reference to the array of the winning
 # board which we can then submit to calculate_score.
 my $winner_found = 0;
 
 until ($winner_found) {
     $turn++;
     printf "turn: %2d, ", $turn;
     $number = shift( @numbers );
     play_turn($number, \@boards, \%state);
     $winner_found = check_for_winner(\@boards, \%state);
     unless (@numbers) { # if we run out of numbers
         say "Out of numbers.  No winner found.";
         last;
     }
 }
 my $score = calculate_score($number, $winner_found, \%state);
 say "winning score is $score";