submission_week_1.erl

-module(submission).
-export([bits/1, bitsTail/1, area/1, perimeter/1, enclose/1]).

% Direct recursive definition of bits func.
bits(0) -> 0;
bits(1) -> 1;
bits(N) when (N > 1) -> N rem 2 + bits(N div 2).

% Tail version of the bits func.
bitsTail(N) -> bitsTailIt(N, 0).
bitsTailIt(0, Acc) -> Acc;
bitsTailIt(N, Acc) -> bitsTailIt(N div 2, Acc + (N rem 2)).

% Shapes
perimeter({circle, {_X, _Y}, R}) ->
  2 * math:pi() * R;
perimeter({rectangle, H, W}) ->
  2 * (H + W);
perimeter({triangle, {A, B}, {C, D}, {E, F}}) ->
  S1 = math:sqrt(square(A - C) + square(B - D)),
  S2 = math:sqrt(square(A - E) + square(B - F)),
  S3 = math:sqrt(square(C - E) + square(D - F)),
  S1 + S2 + S3.

area({circle, {_X, _Y}, R}) ->
  math:pi() * square(R);
area({rectangle, H, W}) ->
  H * W;
area({triangle, {A, B}, {C, D}, {E, F}}) ->
  S1 = math:sqrt(square(A - C) + square(B - D)),
  S2 = math:sqrt(square(A - E) + square(B - F)),
  S3 = math:sqrt(square(C - E) + square(D - F)),
  S = (S1 + S2 + S3) / 2,
  math:sqrt(S*(S - S1)*(S - S2)*(S - S3)).

% Smallest rectangle for a Shape
enclose({circle, {_X, _Y}, R}) ->
  {rectangle, 2*R, 2*R};
enclose({rectangle, H, W}) ->
  {rectangle, H, W};
enclose({triangle, {A, B}, {C, D}, {E, F}}) ->
  Highest = max(B, max(D, F)),
  Shortet = min(B, min(D, F)),
  Leftest = min(A, min(C, E)),
  Rightest = max(A, max(C, E)),
  H = (Highest - Shortet),
  W = (Rightest - Leftest),
  {rectangle, H, W}.

% Util
square(X) -> X * X.

submission_week_1_test.erl

-module(submission_test).
-include_lib("eunit/include/eunit.hrl").
-import(submission, [bits/1, bitsTail/1, area/1, perimeter/1, enclose/1]).

isClose(N1, N2) ->
  abs(N1 - N2) < 0.01.

bits_test() ->
  ?assertEqual(3, bits(7)),
  ?assertEqual(1, bits(8)),
  ?assertEqual(0, bits(0)),
  ?assertEqual(2, bits(5)).

bitsTail_test() ->
  ?assertEqual(3, bitsTail(7)),
  ?assertEqual(1, bitsTail(8)),
  ?assertEqual(0, bitsTail(0)),
  ?assertEqual(2, bitsTail(5)).

% Area and perimeter for a circle
circle_test() ->
  Circle = {circle, {0, 0}, 2},
  ?assert(isClose(area(Circle), 12.56)),
  ?assert(isClose(perimeter(Circle), 12.56)).

% Area and perimeter for a rectangle
rectangle_test() ->
  Rectangle = {rectangle, 2, 4},
  ?assert(isClose(area(Rectangle), 8)),
  ?assert(isClose(perimeter(Rectangle), 12)).

% Area and perimeter for a triangle
triangle_test() ->
  Triangle = {triangle, {0, 0}, {0, 3}, {2, 0}},
  ?assert(isClose(perimeter(Triangle), 8.60)),
  ?assert(isClose(area(Triangle), 3)).

% Small enclosing rectangle
enclose_test() ->
  Circle = {circle, {0, 0}, 2},
  Rectangle = {rectangle, 2, 4},
  Triangle = {triangle, {0, 0}, {0, 3}, {2, 0}},
  ?assertMatch({rectangle, 4, 4}, enclose(Circle)),
  ?assertMatch({rectangle, 2, 4}, enclose(Rectangle)),
  ?assertMatch({rectangle, 3, 2}, enclose(Triangle)).