From 0248ed34ce3d05228bc5084669c3a27933be0c2e Mon Sep 17 00:00:00 2001
From: Nathan Lasseter <nathan.je.lasseter@googlemail.com>
Date: Sun, 4 Oct 2009 00:56:56 +0100
Subject: first commit

---
 problem3.erl | 50 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 50 insertions(+)
 create mode 100755 problem3.erl

(limited to 'problem3.erl')

diff --git a/problem3.erl b/problem3.erl
new file mode 100755
index 0000000..3d8a3b3
--- /dev/null
+++ b/problem3.erl
@@ -0,0 +1,50 @@
+-module(problem3).
+-export([solve/0]).
+
+solve() -> whittle(600851475143,[2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97],1).
+
+whittle(Num,List,Max) ->
+	Q = will_divide(Num, List),
+	if
+		Num =:= 1 ->
+			Max;
+		Q ->
+			H = which_divides(Num,List),
+			if
+				H > Max ->
+					whittle(Num div H, List, H);
+				true ->
+					whittle(Num div H, List, Max)
+			end;
+		true ->
+			whittle(Num, gen_next(List), Max)
+	end.
+			
+
+gen_next(List) ->
+	gen_next(List, lists:max(List) + 1).
+gen_next(List, Next) ->
+	Q = will_divide(Next, List),
+	if
+		Q ->
+			gen_next(List, Next + 1);
+		true ->
+			List ++ [Next]
+	end.
+
+will_divide(_, []) ->
+	false;
+will_divide(Num, [H|T]) ->
+	if
+		Num rem H =:= 0 ->
+			true;
+		true ->
+			will_divide(Num, T)
+	end.
+which_divides(Num, [H|T]) ->
+	if
+		Num rem H =:= 0 ->
+			H;
+		true ->
+			which_divides(Num, T)
+	end.
-- 
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