# RogerBW's Blog

 Perl Weekly Challenge 61: maximum products and IPv4 20 May 2020 I’ve been doing the Perl Weekly Challenges. The latest involved searching for the maximum product in a sequence, and un-munging IPv4 addresses. Given a list of 4 or more numbers, write a script to find the contiguous sublist that has the maximum product. The length of the sublist is irrelevant; your job is to maximize the product. Example Input: [ 2, 5, -1, 3 ] Output: [ 2, 5 ] which gives maximum product 10. Why? This combines two things for which I already have standard patterns: "doubly iterate over a list" and "keep the maximum value and the parameters used to generate it". All quite straightforward. ``````my (\$mxp,\$a,\$b); foreach my \$ai (0..\$#list) { foreach my \$bi (\$ai..\$#list) { my \$p=1; map {\$p*=\$_} @list[\$ai..\$bi]; if (!defined \$mxp || \$p > \$mxp) { (\$mxp,\$a,\$b)=(\$p,\$ai,\$bi); } } } print join(' * ',@list[\$a..\$b]),' = ',\$mxp,"\n"; `````` Raku differs only in details of syntax. You are given a string containing only digits (0..9). The string should have between 4 and 12 digits. Write a script to print every possible valid IPv4 address that can be made by partitioning the input string. For the purpose of this challenge, a valid IPv4 address consists of four “octets” i.e. A, B, C and D, separated by dots (.). Each octet must be between 0 and 255, and must not have any leading zeroes. (e.g., 0 is OK, but 01 is not.) Example Input: 25525511135, Output: 255.255.11.135 255.255.111.35 And this ends up being a standard search with ring buffer. Each entry consists of the octets approved so far, and any remaining matter at the end. The remaining matter is parsed to see if a new octet can be extract from it. ``````my @buf=([\$in]); while (my \$t=shift @buf) { my @l=@{\$t}; my \$r=pop @l; if (\$r eq '' && scalar @l == 4) { print join('.',@l),"\n"; } if (scalar @l >= 4) { next; } foreach my \$fl (1..min(3,length(\$r))) { my \$a=substr(\$r,0,\$fl); `````` One could do this bit with regular expressions, but this seemed cleaner: the number is not greater than 255, and either it's zero or it doesn't start with a zero. `````` if (\$a <= 255 && (\$a==0 || \$a =~ /^[1-9]/)) { my \$b=substr(\$r,\$fl); push @buf,[@l,substr(\$r,0,\$fl),\$b]; } } } `````` I didn't do this one in Raku - that whole list-of-lists thing is a pain, because the language keeps trying to be clever and infer what I want. If I used Raku for anything other than these challenges, I'd settle down and work out just how to get a plain old mutable list of mutable lists with no sugar involved… but I don't, because while parts of the language are great fun to use it's so curst slow as soon as it gets down to anything useful. 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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