Re: Yet another Algorithm::Diff question

[chipmunk]

The 'n' is at line 9 instead of line 8 because at that point you've removed 2 elements and added 3, shifting everything after that up by one.

Solution: apply your changes starting at the end of the array, and work towards the beginning.

[extremely]

Exactly, or keep a line offset counter and work forward!

--
$you = new YOU;
honk() if $you->love(perl)

[chipmunk]

Oh, that won't work either... It looks like the - instructions are indexes into the original array, while the + instructions are indexes into the new array... Try this:

First, process all the delete instructions, starting at the end. Then, process all the insert instructions, starting at the beginning.

I tested that by hand and it came out properly.

[mdillon]

here's my code for it:

#!/usr/bin/perl -w

use strict;

use Data::Dumper;

use Algorithm::Diff qw(diff);

my @orig = qw(a b c e h j l m n p);
my @rev = qw(b c d e f j k l m r s t);

print "Original:\t@orig\n";
print "Revision:\t@rev\n";

my $diff = diff \@orig, \@rev;

my @adds;

for my $hunk (reverse @$diff)
{
    for my $change (reverse @$hunk)
    {
        if($change->[0] eq "-")
        {
            # process deletions
            splice @orig, $change->[1], 1;
        }
        elsif ($change->[0] eq "+")
        {
            # defer handling additions
            unshift @adds, $change;
        }
    }
}

# process additions
splice @orig, $_->[1], 0, $_->[2] for @adds;

print "Patched:\t@orig\n";