我正在寻找更有效算法的建议,以确定数组是否包含从1到数组长度的所有值。我设计的解决方案使用Ada2012正常工作。
------------------------------------------------------------------
-- Build a function to determine whether an array contains --
-- all the values from 1 through the length of the array. --
------------------------------------------------------------------
with Ada.Text_IO; use Ada.Text_IO;
procedure Sequence_test is
type Sequence_Array is array(Positive range <>) of Integer;
function Is_Sequence(Item : Sequence_Array) return Boolean is
Flags : Array(Positive range 1..Item'Length) of Boolean := (Others => False);
begin
for Num of Item loop
if Num in Flags'Range then
Flags(Num) := True;
else
exit;
end if;
end loop;
return (for all P of Flags => P = True);
end Is_Sequence;
A : Sequence_Array := (1,2,3,4,5,6);
B : Sequence_Array := (6,5,4,3,2,1);
C : Sequence_Array := (1,1,1,6,6,6);
D : Sequence_Array := (1,2,3,4,6);
E : Sequence_Array := (6,1,5,2,4,3);
F : Sequence_Array := (1,1,1,2,3,4,5,9,10,11);
begin
Put_Line("A is " & Boolean'Image(Is_Sequence(A)));
Put_Line("B is " & Boolean'Image(Is_Sequence(B)));
Put_Line("C is " & Boolean'Image(Is_Sequence(C)));
Put_Line("D is " & Boolean'Image(Is_Sequence(D)));
Put_Line("E is " & Boolean'Image(Is_Sequence(E)));
Put_Line("F slice is " & Boolean'Image(Is_Sequence(F(3..7))));
end Sequence_test;
我的程序输出
A is TRUE
B is TRUE
C is FALSE
D is FALSE
E is TRUE
F slice is TRUE
答案 0 :(得分:3)
你可以使用一些内置的set support。我认为它不能保证更快地执行,但是如果你打开完全优化并且编译器的优化器是好的,它可能执行得更快。我这样说是因为它可以打包你的数组并一次比较32个bool,而不需要为每个数组进行循环迭代。同样,也可以一次创建你的比较数组32。
当然,如果你的优化器真的好,它可能会弄清楚如何用你的代码做同样的事情。
function Is_Sequence(Item : Sequence_Array) return Boolean is
All_There constant : Array(Positive range 1..Item'Length) of Boolean
:= (Others => True);
Flags : Array(Positive range 1..Item'Length) of Boolean := not All_There;
begin
for Num of Item loop
if Num in Flags'Range then
Flags(Num) := True;
else
exit;
end if;
end loop;
return Flags = All_There;
end Is_Sequence;
我给你的另一个建议就是用return False;
替换那个退出语句你知道那时它不匹配,所以在例程中没有任何意义并且做更多工作。
答案 1 :(得分:2)
在我的电脑上,我用
获得了更好的结果 for Num of Item loop
exit when Num not in Flags'Range;
Flags(Num) := True;
end loop;
return (for all P of Flags => P);
更令人惊讶的是,一个命名的子类似乎可以提供更好的结果:
type Item_Length_Array is array(Positive range 1..Item'Length) of Boolean;
Flags : Item_Length_Array := (others => False);
经过测试:
Start_Time := Ada.Real_Time.Clock;
for I in 1..10_000_000 loop
Ignore := Is_Sequence(A);
Ignore := Is_Sequence(B);
Ignore := Is_Sequence(C);
Ignore := Is_Sequence(D);
Ignore := Is_Sequence(E);
Ignore := Is_Sequence(F(3..7));
end loop;
End_Time := Ada.Real_Time.Clock;