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最新推荐文章于 2021-05-22 22:06:58 发布

原创最新推荐文章于 2021-05-22 22:06:58 发布 · 1.7k 阅读

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#erlang #query #integer #fun #string #include

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本文深入探讨了编程中常用的数据结构与算法实现方法，包括列表反转、元素划分、属性提取、IPv4地址解析等核心操作，同时展示了如何通过自定义函数解决实际问题。文章还涉及了日期判断、字符串分割、日期查询历史记录等功能，旨在为开发者提供全面的技术解决方案。

4. [1,2,3,...,5] ->[5,...,3,2,1] (not use lists:reverse)

reverse(L) -> reverse(L, []).

reverse([], Acc) -> Acc;
reverse([H|T], Acc) -> reverse(T, [H|Acc]).

方法二：

f([H|T]) ->
	f(T) ++ [H];
f([]) -> [].

5. [1,a,"s","d",3,b]->[1,3],[a,b],["s","d"]

split(L) ->
    split(L, [], [], []).

split([H|T], I, A, S) ->
    if
	is_integer(H) -> split(T, [H|I], A, S);
	is_atom(H) -> split(T, I, [H|A], S);
	is_list(H) -> split(T, I, A, [H|S])
    end;
split([], I, A, S) -> [lists:reverse(I), lists:reverse(A), lists:reverse(S)].

6. L=[{Name,Value},...]
   e.g.
   L=[{high, 4},{width,6},{weight,16}]

   4=fun(L,high)
   6=fun(L,width)
   undefined=fun(L,high1)

   What is fun/2?   (not use lists:xxxx )

myfun([], _) ->
    undefined;
myfun([{Target, Value}|_], Target) -> 
    Value;
myfun([_ | T], Target) ->	 
    myfun(T, Target).
test1() ->
    L =[{high, 4},{width,6},{weight,16}],
    [myfun(L, high), myfun(L, width), myfun(L, weight), myfun(L, high1)].

7. decode IPv4 adddress
str_to_ipv4("150.236.11.1")->{150,236,11,1}
str_to_ipv4("150.236.1234.1")->{error, bad_format}

check_ipv4_addr_value(S) ->
    {X, _} = string:to_integer(S),
    case (X >= 0) and (X =< 255) of
	true -> X;
 	_ ->
 	    throw(bad_format)
    end.

str_to_ipv4(Str) ->
    L = string:tokens(Str, "."),
    case (length(L) =:= 4) of
	true ->
	    str_to_ipv4(L, []);
	_ ->
	    {error, bad_format}
    end.

str_to_ipv4([], R) ->
    list_to_tuple(lists:reverse(R));
str_to_ipv4([H|T], R) ->
    try  check_ipv4_addr_value(H) of
	 X ->
	    str_to_ipv4(T, [X|R])
    catch
	throw:bad_format ->
	    {error, bad_format}
    end.

test() ->
    [str_to_ipv4("150.236.11.1"), 
     str_to_ipv4("150.236.1234.1"), 
     str_to_ipv4("1.1.1.1.1")].

8. split words.
   split("Ah, I have a    dream!") ->["Ah","I","have","a","dream"].

9. check the year is leap-year or not.
   Please google the leap-year rule.

   is_leap_year(Int): true|false

10. leap year server. leap_svr.erl
   1) allow customer to query the year is leap year or not.
      query(Int): true|false

   2) record the query history.
      Include the year number be queried.
      e.g. 1998,2002,2340,12453.
   3) allow cusotmer to query the query hisoty.
      history(): [1998,2002,...]