Beefy Boxes and Bandwidth Generously Provided by pair Networks
Don't ask to ask, just ask
 
PerlMonks  

comment on

( #3333=superdoc: print w/replies, xml ) Need Help??
For starters,
use strict; use warnings; sub _unsigned_to_signed { return unpack('i', pack('I', $_[0])); } sub binsearch(&$\@) { my ($compare, $value, $array) = @_; # # If the $value is not found in @array, # the 1s complement of where the $value # should be inserted is returned. So, # $value is found if the return value >= 0. # # When compare is called, $a is an alias for $value, # and $b is an alias for the element of the array # against which $a which be compared. # # Example: # # Add $value to sorted @array, if it's not already there. # $idx = binsearch { $a <=> $b } $value, @array; # splice(@array, ~$idx, 0, $value) if $idx < 0; # my $i = 0; my $j = $#$array; return $j if $j == -1; my $ap = do { no strict 'refs'; \*{caller().'::a'} }; my $bp = do { no strict 'refs'; \*{caller().'::b'} }; my $kp = do { no strict 'refs'; \*{caller().'::k'} }; local *$ap; local *$bp; local *$kp; *$ap = \$value; for (;;) { my $k = int(($j-$i)/2) + $i; *$kp = \$k; *$bp = \($array->[$k]); my $cmp = &$compare(); return $k if $cmp == 0; if ($cmp < 0) { $j = $k-1; return _unsigned_to_signed(~$k) if $i > $j; } else { $i = $k+1; return _unsigned_to_signed(~$i) if $i > $j; } } } our $k; for ( # 0 1 2 3 4 5 6 7 8 [ [qw( a b c p q r x w z )], 'p', 'r', 3, 5, 3 ], [ [qw( a b c p q r x w z )], 'd', 'w', 3, 5, 3 ], [ [qw( q q q q q q q q q )], 'p', 'z', 0, 8, 9 ], [ [qw( q q q q q q q q q )], 'q', 'z', 0, 8, 9 ], [ [qw( q q q q q q q q q )], 'r', 'z', 9, 8, 0 ], [ [qw( q q q q q q q q q )], 'a', 'p', 0, -1, 0 ], [ [qw( q q q q q q q q q )], 'a', 'q', 0, 8, 9 ], [ [qw( q q q q q q q q q )], 'a', 'r', 0, 8, 9 ], ) { my ( $array, $beg, $end, $expect_beg_idx, $expect_end_idx, $expect_count ) = @$_; my $beg_idx = binsearch { $a cmp $b || ( $k > 0 && $a eq $array->[$k-1] ? -1 : 0 ) } $beg, @$array; $beg_idx = ~$beg_idx if $beg_idx < 0; my $end_idx = binsearch { $a cmp $b || ( $k < $#$array && $a eq $array->[$k+1] ? +1 : 0 ) } $end, @$array; $end_idx = ~$end_idx - 1 if $end_idx < 0; my $count = $end_idx - $beg_idx + 1; printf("%2d %-5s %2d %-5s %2d %-5s\n", $beg_idx, $beg_idx == $expect_beg_idx ? "(ok)" : "(bad)", $end_idx, $end_idx == $expect_end_idx ? "(ok)" : "(bad)", $count, $count == $expect_count ? "(ok)" : "(bad)", ); }
3 (ok) 5 (ok) 3 (ok) 3 (ok) 5 (ok) 3 (ok) 0 (ok) 8 (ok) 9 (ok) 0 (ok) 8 (ok) 9 (ok) 9 (ok) 8 (ok) 0 (ok) 0 (ok) -1 (ok) 0 (ok) 0 (ok) 8 (ok) 9 (ok) 0 (ok) 8 (ok) 9 (ok)

It can be optimised, of course. In particular, the negating can be removed, the callback can be inlined, and the initial cuts can be used for both searches.


In reply to Re: Modified Binary Search by ikegami
in thread Modified Binary Search by Limbic~Region

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post; it's "PerlMonks-approved HTML":



  • Are you posting in the right place? Check out Where do I post X? to know for sure.
  • Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:
    <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>
  • Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
  • Want more info? How to link or or How to display code and escape characters are good places to start.
Log In?
Username:
Password:

What's my password?
Create A New User
Chatterbox?
and the web crawler heard nothing...

How do I use this? | Other CB clients
Other Users?
Others meditating upon the Monastery: (4)
As of 2021-06-16 19:24 GMT
Sections?
Information?
Find Nodes?
Leftovers?
    Voting Booth?
    What does the "s" stand for in "perls"? (Whence perls)












    Results (78 votes). Check out past polls.

    Notices?