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Re^2: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1

by tybalt89 (Prior)
on Feb 06, 2019 at 06:31 UTC ( #1229454=note: print w/replies, xml ) Need Help??


in reply to Re: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1
in thread Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1

Would this work if

1) There is no 0 in the list ?

2) There are several 0, Would it pick the correct (earliest) one ?

  • Comment on Re^2: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1

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Re^3: Fastest way to sort a list of integers into 0,1,2,3,-3,-2,-1
by swl (Vicar) on Feb 06, 2019 at 23:58 UTC

    Thanks for checking.

    It fails if there were three or more zeroes (the test case provided has two zeroes), and if there are no zeroes.

    Adding some extra checks seems to fix the issues, and is still close to try1a for speed given the provided test data (sometimes as fast but usually a few percent slower).

    swl2 => sub { my @list = @input; use List::MoreUtils 0.428; @list = sort {$a<=>$b} @list; my $i = List::MoreUtils::bsearchidx {$_ <=> 0} @list; if ($i < 0) { # no zero $i = List::MoreUtils::firstidx {$_ >= 0} @list; } else { $i-- while !$list[$i]; $i++; } push @list, splice @list, 0, $i; Compare(\@list,\@output) or die "@list" if DO_CHECK; },

    It will be slower in cases where there are no zeroes, although List::BinarySearch::binsearch_pos could be used to find an insert point for zero in such cases.

      Another update to handle lists where all values are >= 0 (as flagged in 1229492). Also using the while loop instead of List::MoreUtils::firstidx based on the benchmarks in that post.

      EDIT - added check for upper bound being >=0, borrowing from code in 1229437.

      swl3 => sub { my @list = @input; use List::MoreUtils 0.428; @list = sort {$a<=>$b} @list; if ($list[0] < 0 && $list[-1] >= 0) { my $i = List::MoreUtils::bsearchidx {$_ <=> 0} @list; if ($i < 0) { # no zero, find first positive $i = 0; $i++ while ($list[$i]<0); } else { # find start of zeroes $i-- while !$list[$i]; $i++; } push @list, splice @list, 0, $i; } Compare(\@list,\@output) or die "@list" if DO_CHECK; },

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