Code Golf: Grid Computing

A new puzzle went up on Code Golf a few weeks ago and I finally got some time to sit down and hack on it, so here’s another annotated instalment of my pruning process. I haven’t gotten anywhere near the smallest solutions which are half of my 109 characters. See the action below, but don’t look if you don’t want hints!

Initially, a straightforward for loop that reads from standard input or a passed file; huzzah for Perl’s built-in flexibility. Within this loop, a counter, $n, is incremented to fill an array, @c, with the sum of each column; the sum of the row is stored in $r. At the end of each iteration of the loop, the greatest row sum, $a, is set to the just-completed row if said row is greater than what has been seen previously or the answer is undef, as it is the first time through. The lower loop puts the greatest column sum into $b.

My first pass through is 190 characters:

for (<>) {
    $n = $r = 0;
    for (split ' ', $) {
        @c[$n] += $;
        $r += $_;
        $n++;
    }

1
$a = $r if ($r > $a);



}

for (@c) {
    $b = $_ if ($_ > $b);
}

($b > $a) ? print $b.$/ : print $a.$/;

Note that Perl is flexible; by using <>, input can be passed as a file on the command line or via stdin. With some quick re-ordering of the top loop and turning the lower loop into a map, 20 characters are saved. 170 characters:

for (<>) {
    $n = $r = 0;
    @c[$n++] += $, $r += $ for (split ' ', $_);

1
$a = $r if ($r > $a);



}

map {$b = $_ if ($_ > $b)} @c;

($b > $a) ? print $b.$/ : print $a.$/;

Much of the whitespace can be removed (though I’ll leave the newlines for now). Down to 138 characters:

for(<>){
    $n=$r=0;
    @c[$n++]+=$, $r+=$ for split' ',$_;
    $a=$r if $r>$a;
}


map{$b=$_ if $_>$b} @c;

$b>$a ? print $b.$/ : print $a.$/;

The print can be simplified, dropping 6 characters:

for(<>){
    $n=$r=0;
    @c[$n++]+=$, $r+=$ for split' ',$_;
    $a=$r if $r>$a;
}


map{$b=$_ if $_>$b} @c;

print $b>$a ? $b.$/ : $a.$/;

At which point I’m stuck. After beating out the last bits of whitespace, that is 109 characters.