RogerBW's Blog

 The Weekly Challenge 197: Move with a Wiggle 31 December 2022 I’ve been doing the Weekly Challenges. The latest involved list filtering and a perverse sort. (Note that this is open until tomorrow.) Task 1: Move Zero You are given a list of integers, `@list`. Write a script to move all zero, if exists, to the end while maintaining the relative order of non-zero elements. Here I borrow an idea from atomic theory: a freshly-minted zero is just the same thing as a zero that was in the list. So I construct the list of non-zero values, then push onto the end the right number of zeroes. Rust: ``````fn movezero(l: Vec) -> Vec { let t = l.len(); `````` Here are all the non-zeroes. `````` let mut o: Vec = l.into_iter().filter(|i| *i != 0).collect(); `````` And here are the zeroes. `````` o.append(&mut vec![0; t-o.len()]); o } `````` In PostScript I took a different approach: fill an array of the right length with zeroes, and then copy the non-zero values into the start of it. ``````/movezero { 1 dict begin /i exch def [ i length { 0 } repeat ] dup 0 i { 0 ne } filter putinterval end } bind def `````` Task 2: Wiggle Sort You are given a list of integers, `@list`. Write a script to perform Wiggle Sort on the given list. Wiggle sort would be such as `list[0] < list[1] > list[2] < list[3]....` There can of course be multiple valid answers (e.g. `[1, 2, 3]` could be wigglesorted either as `[1, 3, 2]` or as `[2, 3, 1]`). So the first step in testing was to write something to detect a wigglesorted list. Perl: ``````sub is_wigglesorted(\$l) { foreach my \$i (0..scalar @{\$l}-2) { if (\$i % 2 == 0) { if (\$l->[\$i] >= \$l->[\$i+1]) { return 0; } } else { if (\$l->[\$i] <= \$l->[\$i+1]) { return 0; } } } return 1; } `````` Then it's a matter of doing the sort. This is mostly a matter of taking the sorted list, splitting it in two at the midpoint, then taking one value from each sublist in alternation. But this is rather more fiddly if there's an odd number of values - not given in the example cases but it seemed worth accounting for. Still Perl: ``````sub wigglesort(\$l) { my @s = sort @{\$l}; `````` Get length and split point. `````` my \$le = scalar @s; my \$p = int(\$le / 2); `````` Do the split. `````` my @a = @s[0 .. \$p - 1]; my @b = @s[\$p .. \$#s]; my \$i = 0; my @o; `````` If we have an odd length, take the first value from `b` and put it on the output. `````` if (\$le % 2 == 1) { push @o,\$s[\$p]; @b = @s[\$p + 1 .. \$#s]; \$i = 1; } `````` Then alternate lists. `````` foreach my \$j (\$i .. \$#s) { if (\$j % 2 == 0) { push @o, pop @a; } else { push @o, pop @b; } } return \@o; } `````` Full code on github. Comments on this post are now closed. If you have particular grounds for adding a late comment, comment on a more recent post quoting the URL of this one. Search 10 per page 20 per page 50 per page 100 per page Archive Tags 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s 2000s 2010s 3d printing action advent of code aeronautics aikakirja anecdote animation anime army astronomy audio audio tech aviation base commerce battletech beer boardgaming book of the week bookmonth chain of command children chris chronicle church of no redeeming virtues cold war comedy computing contemporary cornish smuggler cosmic encounter coup covid-19 crime crystal cthulhu eternal cycling dead of winter doctor who documentary drama driving drone ecchi economics en garde espionage essen 2015 essen 2016 essen 2017 essen 2018 essen 2019 essen 2022 essen 2023 existential risk falklands war fandom fanfic fantasy feminism film firefly first world war flash point flight simulation food garmin drive gazebo genesys geocaching geodata gin gkp gurps gurps 101 gus harpoon historical history horror hugo 2014 hugo 2015 hugo 2016 hugo 2017 hugo 2018 hugo 2019 hugo 2020 hugo 2021 hugo 2022 hugo 2023 hugo 2024 hugo-nebula reread in brief avoid instrumented life javascript julian simpson julie enfield kickstarter kotlin learn to play leaving earth linux liquor lovecraftiana lua mecha men with beards mpd museum music mystery naval noir non-fiction one for the brow opera parody paul temple perl perl weekly challenge photography podcast politics postscript powers prediction privacy project woolsack pyracantha python quantum rail raku ranting raspberry pi reading reading boardgames social real life restaurant reviews romance rpg a day rpgs ruby rust scala science fiction scythe second world war security shipwreck simutrans smartphone south atlantic war squaddies stationery steampunk stuarts suburbia superheroes suspense television the resistance the weekly challenge thirsty meeples thriller tin soldier torg toys trailers travel type 26 type 31 type 45 vietnam war war wargaming weather wives and sweethearts writing about writing x-wing young adult Special All book reviews, All film reviews
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