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This module now provides an object-oriented interface that uses less
memory and is easier to use than most of the previous procedural
interfaces.  It also still provides several exportable functions.  We'll
deal with these in ascending order of difficulty:  C<LCS>,
C<LCS_length>, C<LCSidx>, OO interface, C<prepare>, C<diff>, C<sdiff>,
C<traverse_sequences>, and C<traverse_balanced>.

=head2 C<LCS>

Given references to two lists of items, LCS returns an array containing
their longest common subsequence.  In scalar context, it returns a
reference to such a list.

    @lcs    = LCS( \@seq1, \@seq2 );
    $lcsref = LCS( \@seq1, \@seq2 );

C<LCS> may be passed an optional third parameter; this is a CODE
reference to a key generation function.  See L</KEY GENERATION
FUNCTIONS>.

    @lcs    = LCS( \@seq1, \@seq2, \&keyGen, @args );
    $lcsref = LCS( \@seq1, \@seq2, \&keyGen, @args );

Additional parameters, if any, will be passed to the key generation
routine.

=head2 C<LCS_length>

This is just like C<LCS> except it only returns the length of the
longest common subsequence.  This provides a performance gain of about
9% compared to C<LCS>.

=head2 C<LCSidx>

Like C<LCS> except it returns references to two arrays.  The first array
contains the indices into @seq1 where the LCS items are located.  The
second array contains the indices into @seq2 where the LCS items are located.

Therefore, the following three lists will contain the same values:

    my( $idx1, $idx2 ) = LCSidx( \@seq1, \@seq2 );
    my @list1 = @seq1[ @$idx1 ];
    my @list2 = @seq2[ @$idx2 ];
    my @list3 = LCS( \@seq1, \@seq2 );

=head2 C<new>

    $diff = Algorithm::Diffs->new( \@seq1, \@seq2 );
    $diff = Algorithm::Diffs->new( \@seq1, \@seq2, \%opts );

C<new> computes the smallest set of additions and deletions necessary
to turn the first sequence into the second and compactly records them
in the object.

You use the object to iterate over I<hunks>, where each hunk represents
a contiguous section of items which should be added, deleted, replaced,
or left unchanged.

=over 4

The following summary of all of the methods looks a lot like Perl code
but some of the symbols have different meanings:

    [ ]     Encloses optional arguments
    :       Is followed by the default value for an optional argument
    |       Separates alternate return results

Method summary:

    $obj        = Algorithm::Diff->new( \@seq1, \@seq2, [ \%opts ] );
    $pos        = $obj->Next(  [ $count : 1 ] );
    $revPos     = $obj->Prev(  [ $count : 1 ] );
    $obj        = $obj->Reset( [ $pos : 0 ] );
    $copy       = $obj->Copy(  [ $pos, [ $newBase ] ] );
    $oldBase    = $obj->Base(  [ $newBase ] );

Note that all of the following methods C<die> if used on an object that
is "reset" (not currently pointing at any hunk).

    $bits       = $obj->Diff(  );
    @items|$cnt = $obj->Same(  );
    @items|$cnt = $obj->Items( $seqNum );
    @idxs |$cnt = $obj->Range( $seqNum, [ $base ] );
    $minIdx     = $obj->Min(   $seqNum, [ $base ] );
    $maxIdx     = $obj->Max(   $seqNum, [ $base ] );
    @values     = $obj->Get(   @names );

Passing in C<undef> for an optional argument is always treated the same
as if no argument were passed in.

=item C<Next>

    $pos = $diff->Next();    # Move forward 1 hunk
    $pos = $diff->Next( 2 ); # Move forward 2 hunks
    $pos = $diff->Next(-5);  # Move backward 5 hunks

C<Next> moves the object to point at the next hunk.  The object starts
out "reset", which means it isn't pointing at any hunk.  If the object
is reset, then C<Next()> moves to the first hunk.

C<Next> returns a true value iff the move didn't go past the last hunk.
So C<Next(0)> will return true iff the object is not reset.

Actually, C<Next> returns the object's new position, which is a number
between 1 and the number of hunks (inclusive), or returns a false value.

=item C<Prev>

C<Prev($N)> is almost identical to C<Next(-$N)>; it moves to the $Nth
previous hunk.  On a 'reset' object, C<Prev()> [and C<Next(-1)>] move
to the last hunk.

The position returned by C<Prev> is relative to the I<end> of the
hunks; -1 for the last hunk, -2 for the second-to-last, etc.

=item C<Reset>

    $diff->Reset();     # Reset the object's position
    $diff->Reset($pos); # Move to the specified hunk
    $diff->Reset(1);    # Move to the first hunk
    $diff->Reset(-1);   # Move to the last hunk