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Re: Spiraling integers

by demerphq (Chancellor)
on Aug 29, 2005 at 11:55 UTC ( #487380=note: print w/replies, xml ) Need Help??

in reply to Spiraling integers

Non recursive implementation, strict safe, but not warning free. 252 chars.

use strict; sub spiral { my$S=pop;my($z,$s,$t,$d,$x,$y,@b)=($S**2,1);@_=([1, 0],[0,1],[-1,0],[0,-1]);$b[$S][$_]=$b[$_][$S]=$/for 0..$S;map{$b[$y][$x]=sprintf"%0*d",length$z,$_;($s, $t)=@{$_[++$d%4]}if$s&&$b[$y][$x+$s]||$t&&$b[$y+$t] [$x];$x+=$s;$y+=$t}1..$z;pop@b;print"@$_"for@b; } for (1..10) { spiral($_); print "\n---\n"; }

It could go smaller fairly easily by using globals, but then couldnt be run more than once per process.

Update: And here is the annotated version. Funny, while annotating it I noticed a couple of things I could have done to make it smaller :-)

use strict; sub spiral { my $size = pop; # get the size from the arguments my $elements = $size**2; # how many numbers in the square my $dir=0; # we will go right at start my ($dx,$dy)=(1,0); # starting deltas (must match $dir) my ($x,$y)=(0,0); # start top left my @board; # the board we will use my @delta=([1,0], # deltas for going right [0,1], # ... down [-1,0], # ... left [0,-1]); # ... up # Set up sentinal values in (x,$size) and ($size,y) # ie, a column on the right and a row at the bottom $board[$size][$_]=$board[$_][$size]="\n" for 0..$size; # The strategy is to treat $x,$y as a cursor on the grid. # each square we move in the direction specified by $dir # via the @delta table, assuming that is that the new # cell has not been filled already. if it has we turn to # the right by incrementing $dir and finding new deltas. for (1..$elements) { # neatly set up the value in the grid, we use the length of # the center element to determine how many digits to use per " +cell" $board[$y][$x] = sprintf"%0*d",length $elements, $_; # if we bump into something we need to turn to the right # the sentinals mean we dont have to check for anything other # than the cell being nonempty in the direction we are travell +ing ($dx,$dy)=@{$delta[++$dir%4]} if $dx && $board[$y][$x+$dx] || $dy && $board[$y+$dy][$x]; # and adjust our position according to the deltas $x+=$dx; $y+=$dy }; # we need to remove the bottom row as it is just a list of newline +s pop @board; # and now we print it out, we dont need to remove the right hand # sentinals as they conveniently end the line for us. print"@$_" for @board; } for (1..10) { spiral($_); print "\n---\n"; }

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