# RogerBW's Blog

 Perl Weekly Challenge 67: combining numbers and phone keypad 03 July 2020 I’ve been doing the Perl Weekly Challenges. The latest involved generating combinations of numbers and expanding telephone keypad letters. You are given two integers `\$m` and `\$n`. Write a script print all possible combinations of `\$n` numbers from the list 1 2 3 … `\$m`. Every combination should be sorted i.e. [2,3] is valid combination but [3,2] is not. Example: Input: `\$m = 5, \$n = 2` Output: `[ [1,2], [1,3], [1,4], [1,5], [2,3], [2,4], [2,5], [3,4], [3,5], [4,5] ]` Oh well, it was nice while it lasted. Back to the BFS-with-FIFO-buffer mine. On the other hand we can at least use the `is_deeply` structure comparator of `Test::More`. ``````use Test::More tests => 2; is_deeply(combine(5,2), [ [1,2], [1,3], [1,4], [1,5], [2,3], [2,4], [2,5], [3,4], [3,5], [4,5] ], 'expansion 5 2', ); is_deeply(combine(4,3), [ [1,2,3], [1,2,4], [1,3,4], [2,3,4] ], 'expansion 4 3', ); sub combine { my (\$m,\$n)=@_; my @out; my @a; do { my \$s=[]; if (@a) { \$s=shift @a; } `````` If there's a slot left open, fill it with each possible value. Otherwise, append the complete answer to the output buffer. `````` if (scalar @{\$s} < \$n) { my \$base=0; if (@{\$s}) { \$base=\$s->[-1]; } foreach my \$k (\$base+1..\$m) { push @a,[@{\$s},\$k]; } } else { push @out,\$s; } } while @a; return \@out; } `````` Can't be bothered to do this in Raku. Nor the next one. You are given a digit string `\$S`. Write a script to print all possible letter combinations that the given digit string could represent. (This uses standard ITU E 1.161 lettering as found on most phone keypads.) More BFS/FIFO. This is in fact nearly the same problem as in part one, except that we're meant to produce a list of strings rather than a list of lists of numbers. So we solve it the same way. ``````use Test::More tests => 1; is_deeply(expand('35'), ["dj", "dk", "dl", "ej", "ek", "el", "fj", "fk", "fl"], 'expansion 35', ); sub expand { my (\$digits)=@_; my %table=( 2 => [qw(a b c)], 3 => [qw(d e f)], 4 => [qw(g h i)], 5 => [qw(j k l)], 6 => [qw(m n o)], 7 => [qw(p q r s)], 8 => [qw(t u v)], 9 => [qw(w x y z)], ); `````` The problem doesn't specify, but I assume that characters without a letter-equivalent are ignored. `````` my @d=grep {exists \$table{\$_}} split '',\$digits; my @out; my @a; do { my \$s=[]; if (@a) { \$s=shift @a; } my \$l=scalar @{\$s}; if (\$l <= \$#d) { foreach my \$dx (@{\$table{\$d[\$l]}}) { push @a,[@{\$s},\$dx]; } } else { push @out,join('',@{\$s}); } } while @a; return \@out; } `````` It might have been a little more interesting if the results had had to be checked against a list of valid words, so that for example 7375 would produce only "perk" and "serk" (the Middle English ancestor of "sark") rather than all 144 possibilties. 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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