I'd write it this way: (apply + (mapcat #(range 1 %) (range 2 14))) I think idiomatically I would have written it with (partial range 1) instead of #(range 1 %), but I prefer compact forms.
Mibu On Dec 24, 8:57 pm, MattyDub <mattydu...@gmail.com> wrote: > I was presented with the question "How many gifts, total, are > mentioned in the song 'The 12 Days of Christmas'?" I thought, "Aha! > I'll use clojure to figure it out." But I wanted to do it > idiomatically, using some functional constructs (with which I'm not > very familiar). First, I needed to know how many presents were given > on day n: > (defn sum-up-to [n] > "returns the sum of the positive integers from 1 to n" > (apply + 0 > (map #(+ 1 %) (range n)))) > > (As an aside, yes, I know this is the same series from the apocryphal > story about Gauss as a child, and that the result is n+1/(n/2), but > using that would defeat the purpose of learning these functional > constructs). > The "apply + 0" is a little wonky, though, yes? I think that > reduce would be better, right? So I change the function: > (defn sum-up-to [n] > "returns the sum of the positive integers from 1 to n" > (reduce + (map #(+ 1 %) (range n)))) > > Then we need to find the sum of each of those days, from 1 to 12; > first, let's get that sequence (just to make sure I'm doing it right), > then let's add it up: > user> (map sum-up-to (range 1 13)) > (1 3 6 10 15 21 28 36 45 55 66 78) > user> (reduce + (map sum-up-to (range 1 13))) > 364 > > (Originally, I didn't know about the 2-argument version of range, > so I was using map and an anonymous inline function to add 1 to each > result from range, like: > (map #(sum-up-to (inc %)) (range 12)) > Then I thought "This can't be right, there has to be a way to do this > already", and looked at the docs for range. It's nice when you find > something you want already exists - thanks, Rich!) > Fun times - thanks, clojure! > -Matt > PS I'm sure there are versions of this that are shorter (1 line?) or > perform better (e.g., by caching previous sums or something) - but > I'll leave those as an exercise for somebody else. ;) --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
