Re^2: Spreading out the elements

Unfortunately, it turns out that the Bresenham algorithm isn't exactly the right thing - or I've misconscrewed something. Here's my implementation of it, with extra code to detect the crossings; it does a reasonable distribution of the two arrays, but doesn't quite follow the rules that I originally stated:

#!/usr/bin/perl -w
# Created by Ben Okopnik on Wed Jul  4 13:39:28 EDT 2007

# Modified and converted to code from Wikipedia entry for "Bresenham"
sub brezzie {
    my ($x1, $y1) = @_;
    ($x1, $y1) = ($y1, $x1) if $y1 > $x1;

    my ($deltax, $deltay) = ($x1, $y1);
    my $error = -$deltax / 2;

    my $y = 0;
    my ($last_a, $last_b) = (0, 0);

    for my $x (0 .. $x1){
        # print $steep ? "$y $x\n" : "$x $y\n";
        if ($y1 > $x1){ 
            ($b, $a) = ($x, $y);
        }
        else {
            ($a, $b) = ($y, $x);
        }

        print "A" if $a > $last_a;
        print "B" if $b > $last_b;

        ($last_a, $last_b) = ($a, $b);

        $error += $deltay;

        if ($error > 0){
            $y = $y + 1;
            $error -= $deltax;
        }
    }
}

brezzie(4, 14);
[download]

Running this results in 'BABBBBABBBABBBBABB' - and what I'm looking for is more like 'ABBBBBABBBBABBBBBA'. Max distance is not quite the same thing as a fair distribution.

I really appreciate the help that you've given me so far!

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Re^3: Spreading out the elements by ForgotPasswordAgain (Vicar) on Jul 05, 2007 at 14:02 UTC
I think this is what merlyn means: `perl -MAlgorithm::Line::Bresenham=line -le'($A,$B)=@ARGV;@p=map{$_->[0 +]}line($A,1,1,$B);$l=$p[1];for(1..$B){if($p[$_]==$l){push@a,"A"}else{ +push@a,"B";$l=$p[$_]}}print$_ for@a' 10 40` [download] Sorry, made it on the command line, can't be bothered to reformat it. The idea is to use ($A, 1) for the start point, (1, $B) for the end point, then pluck out the x values (projection of line onto x-axis, if that makes sense) from the list returned by `line`. The x values will sometimes stay the same, sometimes increase; you're interested in where it increases, that's where the Bs get plopped in. I don't think that you'll generally have the exact right number of each element, just that you'll get a roughly even distribution of elements, given a certain ratio of A and B. Quickly experimenting about, I found that it breaks a little when the 1st number approaches the 2nd one (try 990 and 1000, for example, there will be 989 Bs instead of 990) Assumes: two integer args on command line, the first would be your number of Bs, the second the total number of A + B. It doesn't do things you wanted like endpoints always are A. For that, just subtract 2 from 2nd arg, and print out A at the beginning and end.	[reply] [d/l] [select]

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Re^3: Spreading out the elements
by ForgotPasswordAgain (Vicar) on Jul 05, 2007 at 14:02 UTC

I think this is what merlyn means:

perl -MAlgorithm::Line::Bresenham=line -le'($A,$B)=@ARGV;@p=map{$_->[0
+]}line($A,1,1,$B);$l=$p[1];for(1..$B){if($p[$_]==$l){push@a,"A"}else{
+push@a,"B";$l=$p[$_]}}print$_ for@a' 10 40
[download]

Sorry, made it on the command line, can't be bothered to reformat it. The idea is to use ($A, 1) for the start point, (1, $B) for the end point, then pluck out the x values (projection of line onto x-axis, if that makes sense) from the list returned by line. The x values will sometimes stay the same, sometimes increase; you're interested in where it increases, that's where the Bs get plopped in.

I don't think that you'll generally have the exact right number of each element, just that you'll get a roughly even distribution of elements, given a certain ratio of A and B. Quickly experimenting about, I found that it breaks a little when the 1st number approaches the 2nd one (try 990 and 1000, for example, there will be 989 Bs instead of 990)

Assumes: two integer args on command line, the first would be your number of Bs, the second the total number of A + B.

It doesn't do things you wanted like endpoints always are A. For that, just subtract 2 from 2nd arg, and print out A at the beginning and end.

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