Functional Programming in Erlang, assignment 1.24 2017-03-05

one_24.erl

-module(one_24).
-export([bits/1, enclose/1, perimeter/1, tail_bits/1]).

%% perimeter/1 - calculate the perimeter of common shapes
%% circle - πD, unrelated to coordinates
perimeter({circle, {_X,_Y}, Radius}) ->
	Radius * 2 * math:pi();
%% rectangle - assumes coordinate 1 is lower left, coordinate 2 is upper 
%% right, clauses with guards could be used to ensure it
perimeter({rectangle, {X1,Y1}, {X2,Y2}}) ->
	Height = Y2 - Y1,
	Width = X2 - X1,
	Height * 2 + Width * 2;
perimeter({triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}) ->
	%% Use Pythagorean theorem to find side lengths
	L1 = math:sqrt((X2-X1) * (X2-X1) + (Y2-Y1) * (Y2-Y1)),
	L2 = math:sqrt((X3-X2) * (X3-X2) + (Y3-Y2) * (Y3-Y2)),
	L3=  math:sqrt((X1-X3) * (X1-X3) + (Y1-Y3) * (Y1-Y3)),
	L1 + L2 + L3.

%% enclose/1 - find the enclosing rectangle of a given common shape
%% circle = a square centered around the center of the cirle, sides
%% are 1 radius away from the center in all four directions
enclose({circle, {X,Y}, Radius}) ->
	{rectangle, {X-Radius, Y-Radius}, {X+Radius, Y+Radius}};
%% rectangle = the enslosing rectangle of a rectangle is the rectangle
enclose({rectangle, {X1,Y1}, {X2,Y2}}) ->
	{rectangle, {X1,Y1}, {X2,Y2}};
%% triangle = min and max of values of all three coordinates
enclose({triangle, {X1,Y1}, {X2,Y2}, {X3,Y3}}) ->
	{rectangle, {lists:min([X1,X2,X3]),lists:min([Y1,Y2,Y3])}, 
		{lists:max([X1,X2,X3]),lists:max([Y1,Y2,Y3])}}.

%% Use bit shift in math to calculate number of bits set to 1 in an int
%% with an accumulator
tail_bits(N) -> tail_bits(N, 0).
tail_bits(N,Acc) when N < 1 ->
	Acc;
tail_bits(N, Acc) when N rem 2 =:= 1 ->
	tail_bits(trunc(N/2), Acc + 1);  %% use trunc/1 to convert float to int
tail_bits(N, Acc) when N rem 2 =:= 0 ->
	tail_bits(trunc(N/2), Acc).      %% use trunc/1 to convert float to int

%% Use bit shift in math to calculate number of bits set to 1 in an int
bits(0) -> 0;
bits(N) -> 
	N rem 2 + bits(trunc(N/2)).      %% use trunc/1 to convert float to int