# RogerBW's Blog

 The Weekly Challenge 163: Sums and Sums 05 May 2022 I’ve been doing the Weekly Challenges. The latest involved various summation-like operations. (Note that this is open until 8 May 2022.) Task 1: Sum Bitwise Operator You are given list positive numbers, `@n`. Write script to calculate the sum of bitwise & operator for all unique pairs. In other words, bitwise-and each pair of numbers, and return the total. (Why?) For me this was a test of the ease of use of various languages' `combination` and `reduce` functions. For some it was least painful to lay it out in full, such as Kotlin (also Javascript, PostScript, Lua, and as it turned out Rust): ``````fun sumbitwise(ls: List): Int { var s = 0 for (i in 0..ls.size-2) { for (j in i+1..ls.size-1) { s += ls[i] and ls[j] } } return s } `````` while in Raku (and Ruby) it could be a one-liner: ``````sub sumbitwise(@ls) { return @ls.combinations(2).map({\$_[0] +& \$_[1]}).sum; } `````` Perl (with `Algorithm::Combinatorics`) and Python lay somewhere in between. Task 2: Summations You are given a list of positive numbers, `@n`. Write a script to find out the summations as described below. The nth Row starts with the second element of the (n-1)th row. The following element is sum of all elements except first element of previous row. You stop once you have just one element in the row. In other words, repeatedly replace `[a,b,c,d]` with `[b,b+c,b+c+d]` until there's only one element left, and return that. For the five-element examples given, this would come out as `5b+5c+3d+e`, but I worked it out iteratively anyway. I haven't given a PostScript example for one of these for a while: ``````/summation { 2 dict begin /ls exch def { `````` Loop until we've got just one value. `````` ls length 1 eq { exit } if `````` Build a new array consisting of the relevant sums. `````` [ 1 1 ls length 1 sub { /s 0 def 1 exch 1 exch { ls exch get s add /s exch def } for s } for ] /ls exch def } loop `````` Return the first (and only) value in the array. `````` ls 0 get end } bind def `````` More conventionally in Ruby (where `inject` is what it calls `reduce`), but basically the same algorithm: ``````def summation(ls0) ls = ls0 while ls.length > 1 do lv = [] 1.upto(ls.length - 1).each do |i| lv.push((1..i).inject(0) {|sum, n| sum + ls[n]}) end ls = lv end return ls[0] end `````` 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 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
Produced by aikakirja v0.1