Richard,<br><br>Lovely solution! It's stuff like this that helps newcomers to Erlang like myself to learn how to write better Erlang.<br><br>I'm curious, though; what is the reason for writing <br><br>Qs = [integer_to_list(S) || S <- [X*X || X <- lists:seq(32,99)]]<br>
<br>instead of <br><br>Qs = [integer_to_list(X*X) || X <- lists:seq(32,99)]<br><br>?<br><br><div class="gmail_quote">2008/7/6 Richard Carlsson <<a href="mailto:richardc@it.uu.se">richardc@it.uu.se</a>>:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div class="Ih2E3d">Toby Thain wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi list,<br>
<br>
I stumbled on this simple 'puzzle'[0] posted some years ago on comp.lang.tcl (originally to an Icon mailing list).<br>
<br>
After solving it in Icon[1] and SQL[2] I decided to see what an Erlang solution would look like. I'm posting here firstly because other people's solutions would be interesting, and also I'd like to see how my own solution[3] could be improved.<br>
<br>
Any takers over the weekend? :-)<br>
<br>
--Toby<br>
<br>
[0] <a href="http://groups.google.com/group/comp.lang.tcl/msg/8846d9f7491ba0ba" target="_blank">http://groups.google.com/group/comp.lang.tcl/msg/8846d9f7491ba0ba</a><br>
[1] <a href="http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/vn.icn" target="_blank">http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/vn.icn</a><br>
[2] <a href="http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/Makefile" target="_blank">http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/Makefile</a><br>
[3] <a href="http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/erlang/" target="_blank">http://telegraphics.com.au/svn/puzzles/trunk/vier-neun/erlang/</a><br>
</blockquote>
<br></div>
Here's my version. Note that it's often better to think in terms of<br>
stages of list processing (mapreduce etc.), instead of inserting and<br>
looking up in dictionaries. I tag each generated pair with the E<br>
element, just to make the list easier to work with later.<br><font color="#888888">
<br>
/Richard<br>
</font><br>%% File: solve.erl<br>
%% @author Richard Carlsson<br>
<br>
-module(solve).<br>
-export([it/0]).<br>
<br>
%% Problem: VIER and NEUN are 4-digit squares; determine distinct V, I,<br>
%% E, R, N, and U, such that there is a unique solution (VIER,NEUN) for<br>
%% some particular E.<br>
<br>
it() -><br>
Qs = [integer_to_list(S) || S <- [X*X || X <- lists:seq(32,99)]],<br>
Ps = [{E,{Vr,Nn}} || [N,E,_U,N]=Nn <- Qs, [_V,_I,E1,_R]=Vr <- Qs,<br>
E =:= E1,<br>
length(ordsets:from_list(Nn++Vr)) =:= 6],<br>
D = lists:foldl(fun ({E,_}, D) -> dict:update_counter(E,1,D) end,<br>
dict:new(), Ps),<br>
[P || {E,1} <- dict:to_list(D), {E1,P} <- Ps, E=:=E1].<br>
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