Future Learn Erlang Mooc - Week 1

erlang-week1.erl

-module(week1).
-export([perimeter/1,area/1,enclose/1, bitsD/1, bitsT/1]).

% I don't use Erlang Unit test http://erlang.org/doc/apps/eunit/chapter.html
% Because I don't know how to setup a project with dependancies at this point

% Each shape is defined by it's name, some general info and some points
perimeter({circle,R, _CenterPoint}) ->
  2 * math:pi() * R;
perimeter({rectangle,W,H, _Points}) ->
  (H + W) * 2;
perimeter({triangle,A,B,C, _Points}) ->
  (A + B + C).

area({circle,R, _CenterPoint}) ->
  math:pi() * R * R;
area({rectangle,W,H,_Points}) ->
  H * W;
% I use Heron formula for triangle's area http://jwilson.coe.uga.edu/emt725/Heron/Heron.html
area({triangle,A,B,C,_Points}) ->
  S = (A + B + C) / 2,
  math:sqrt(S*(S-A)*(S-B)*(S-C)).

getX({X,_Y}) ->
  X.
getY({_X,Y}) ->
  Y.

% it's maybe a brute force solution :)
% some tests cases :
%  week1:enclose({triangle,1,1,1,[{-12,-10}, {8,8}, {12, 10}]}).
% result == {rectangle,24,20,{-12,10},{12,10},{12,-10},{-12,-10}}
% week1:enclose({rectangle,10,10,[{-5,5},{5,5},{5,-5},{-5,-5}]}).
% result == {rectangle,10,10,{-5,5},{5,5},{5,-5},{-5,-5}}
enclosing_rectangle_of_points(Points) ->
  Xs = lists:map(fun(Point) -> getX(Point) end, Points),
  Xmax = lists:max(Xs),
  Xmin = lists:min(Xs),
  Ys = lists:map(fun(Point) -> getY(Point) end, Points),
  Ymax = lists:max(Ys),
  Ymin = lists:min(Ys),
  {rectangle, (Xmax-Xmin), (Ymax-Ymin), {Xmin, Ymax}, {Xmax, Ymax}, {Xmax, Ymin}, {Xmin, Ymin}}.

enclose({circle,R,CenterPoint}) ->
  Xmax = getX(CenterPoint)+R,
  Xmin = getX(CenterPoint)-R,
  Ymax = getY(CenterPoint)+R,
  Ymin = getY(CenterPoint)-R,
  {rectangle, (Xmax-Xmin), (Ymax-Ymin), {Xmin, Ymax}, {Xmax, Ymax}, {Xmax, Ymin}, {Xmin, Ymin}};
enclose({rectangle,_W,_H,Points}) ->
  enclosing_rectangle_of_points(Points);
enclose({triangle,_A,_B,_C,Points}) ->
  enclosing_rectangle_of_points(Points).

% with direct recursion
bitsD(0) ->
  0;
bitsD(1) ->
  1;
bitsD(N) ->
  % i use log2 and pow2 to find the greatest binary divisor
  % using trunc to get Integer from Float
  BinaryPosition = erlang:trunc(math:log2(N)),
  GreatestDivisor = erlang:trunc(math:pow(2,BinaryPosition)),
  1 + bitsD(N rem GreatestDivisor).

% with tail cail recursion
bitsT(N) ->
  bits(N, 0).

bits(0, Acc) ->
  Acc;
bits(1, Acc) ->
  Acc + 1;
bits(N, Acc) ->
  % i use log2 and pow2 to find the greatest binary divisor
  % using trunc to get Integer from Float
  BinaryPosition = erlang:trunc(math:log2(N)),
  GreatestDivisor = erlang:trunc(math:pow(2,BinaryPosition)),
  bits(N rem GreatestDivisor, Acc+1).

% Some test cases for bits function
% week1:bitsT(63) == 6 == week1:bitsD(63)
% week1:bitsT(35) == 3 == week1:bitsD(35)
% week1:bitsT(32) == 1 == week1:bitsD(32)