Excercise 002

e002.erl

@@ -0,0 +1,52 @@
+% Find the sum of all the even-valued terms in the Fibonacci sequence which do not exceed four million.
+
+% Each new term in the Fibonacci sequence is generated by adding the previous two terms. By starting with 1 and 2, the first 10 terms will be:
+% 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
+% Find the sum of all the even-valued terms in the sequence which do not exceed four million.
+
+-module(e002).
+-export([
+        main/1,
+        fibonacci_max/1
+    ]).
+
+fibonacci_max(Max) ->
+    fibonacci_max_([], Max).
+
+fibonacci_max_([], Max) ->
+    if
+        Max < 1 ->
+            [];
+        true ->
+            fibonacci_max_([1], Max)
+    end;
+fibonacci_max_([N], Max) ->
+    Next = N + N,
+    if
+        Max < Next ->
+            [N];
+        true ->
+            fibonacci_max_([Next, N], Max)
+    end;
+fibonacci_max_([N1, N2 | Seq], Max) ->
+    Next = N1 + N2,
+    if
+        Max < Next ->
+            [N1, N2 | Seq];
+        true ->
+            fibonacci_max_([Next, N1, N2 | Seq], Max)
+    end.
+
+sum_if_even([]) ->
+    0;
+sum_if_even([N | Seq]) ->
+    if
+        N rem 2 == 0 ->
+            N + sum_if_even(Seq);
+        true ->
+            sum_if_even(Seq)
+    end.
+
+main(_) ->
+    Max = 4000000,
+    io:format("Sum for fibonacci <= ~w: ~w~n", [Max, sum_if_even(fibonacci_max(Max))]).