http://www.perlmonks.org?node_id=617807


in reply to Creating a circle in a data structure

Instead of going round the circle, it may be easier to iterate over all values in one direction, i.e. something like:

foreach $ydist ( 0..$radius ) { # using the formula: # xdist*xdist + ydist*ydist = radius*radius $xdist = int(sqrt( $radius*$radius - $ydist*$ydist)); # Take advantage of symmetry to plot 4 points at once # (for circle outline) $circle{$x_center-$xdist}{$y_center-$ydist}++; $circle{$x_center+$xdist}{$y_center-$ydist}++; $circle{$x_center-$xdist}{$y_center+$ydist}++; $circle{$x_center+$xdist}{$y_center+$ydist}++; # Or to fill up the whole disc... foreach $x ( $x_center-$xdist .. $x_center+$xdist ) { $circle{$x}{$y_center-$ydist}++; $circle{$x}{$y_center+$ydist}++; } }

Of course this assumes you're dealing with a grid of integers. Right now it also counts every point on the axis twice but that's easy enough to fix.