用Erlang写了个优惠计算器

由于cnblogs的代码着色系统不支持erlang，所以就直接从博客上贴过来了，如果大家看的不习惯的话，就直接来我的博客上看吧

本文章为本人个人博客相应文章的镜像：

原文地址： http://www.greatony.com/index.php/2010/03/17/cashback-calculator-written-in-erlang/ 

 

今天在为公司买东西的时候，发现了qq的一个网站：QQ返利

后来又发现了新蛋网的qq返利的比率很有意思，最近又在学习erlang，所以就写个程序，看看对于这种算法类的程序，erlang写起来是否麻烦，一下是代码：

01	-module(bne).

02	-export([solve/1, print_solution/1]).

03

04	% Calculate the cashback of a bill

05	get_cashback(N) when N =< 100 -> 0.76;

06	get_cashback(N) when N =< 300 -> 2.29;

07	get_cashback(N) when N =< 500 -> 5.35;

08	get_cashback(N) when N =< 800 -> 7.65;

09	get_cashback(N) when N =< 1000 -> 11.47;

10	get_cashback(N) when N =< 2000 -> 13.0;

11	get_cashback(N) when N =< 3000 -> 16.83;

12	get_cashback(N) when N =< 5000 -> 20.65;

13	get_cashback(N) when N =< 8000 -> 24.48;

14	get_cashback(N) when N =< 10000 -> 34.42;

15	get_cashback(_N) -> 42.07.

16

17	% Calculate the real cost of a bill

18	get_bill_cost({Total, _}) when Total < 99 -> Total + 10.0 - get_cashback(Total);

19	get_bill_cost({Total, _}) -> Total - get_cashback(Total).

20

21	% Calculate the total cost of a solution

22	get_solution_cost(Solution) -> lists:foldl(fun(X, Sum) -> get_bill_cost(X) + Sumend, 0, Solution).

23

24	% make combinations with a series of combination and a new element

25	reduce_comb(HeadList, [], Element) -> [HeadList ++ [[Element]]];

26	reduce_comb(HeadList, [Head | Rest], Element) -> [HeadList ++ [[Element | Head]] ++Rest | reduce_comb(HeadList ++ [Head], Rest, Element)].

27

28	% call Function on each combination of the 3rd argument, and the Default, the return value will overwrite the Default value

29	combination(_Function, Default, []) -> Default;

30	combination(Function, Default, [Head]) -> Function([[Head]], Default);

31	combination(Function, Default, [Head | List]) ->

32	combination(fun(Combination, OldSolution) ->

33	ReducedCombination = reduce_comb([], Combination, Head),

34	lists:foldl(Function, OldSolution, ReducedCombination)

35	end, Default, List).

36

37	% choose a solution from a set of solution

38	choose_solution(Solutions) -> lists:foldl(

39	fun(NewSolution, ExistSolution) ->

40	case NewSolution of

41	{Cost, Solution} ->

42	case ExistSolution of

43	no_solution -> NewSolution;

44	{OldCost, _} when OldCost > Cost -> {Cost, Solution};

45	_ -> ExistSolution

46

end;

47	no_solution -> ExistSolution

48

end

49	end, no_solution, Solutions).

50

51	% solve problem

52	solve([]) -> {ok, 0, []};

53	solve([Price]) -> {ok, get_bill_cost({Price, [Price]}), [[Price]]};

54	solve(PriceList) -> combination(

55	fun(Combination, Origional) ->

56	Solution = lists:map(fun(Bill) -> {lists:sum(Bill), Bill} end,Combination),

57	choose_solution([{get_solution_cost(Solution), Solution} , Origional])

58	end, no_solution, PriceList).

59

60	% print a bill

61	print_bill({Total, Items}) ->

62	io:fwrite("    Bill Total: ~p, Cashback: ~p, Real: ~p~n", [Total, get_cashback(Total), get_bill_cost({Total, Items})]),

63	lists:foreach(fun(Item) -> io:fwrite("        ~p~n", [Item]) end, Items),

64	io:fwrite("~n").

65

66	% print the solution

67	print_solution({Cost, Solution}) ->

68	io:fwrite("Solution Total: ~p, Bill Count: ~p~n", [Cost, length(Solution)]),

69	lists:foreach(fun(Bill) -> print_bill(Bill) end, Solution),

70	io:fwrite("~n").

用法：

1	bne:print_solution(bne:solve([64, 44, 100, 10, 29])).

Erlang确实是个很优秀的语言，特别是解决这种问题的时候。

我几乎就只是在描述问题，而不是在解决问题，虽然这还需要我花一点时间去适应

在下一篇文章里，我会着重讲排列组合的实现方式