如何确定字符串中的所有字符是否相等 [英] How to determine if all characters in a string are equal

问题描述

我需要知道字符串中的所有字符是否相等（由同一个字符组成）。该函数必须返回true或false，这取决于字符串的所有元素是否等于特定的字符。

I need to know if all characters in a string are equal (formed by the same character). the function must return true or false depending if all the elements of the string are equal to an particular char.

我写了这个功能很好，但我正在看对于一个更优化（最快）的解决方案，字符串可以有数千个字符。

I wrote this function that works well, but I'm looking for a more optimal (fastest) solution, the strings can have thousands of chars.

function AllElementsAreEqual(Element:Char;Str:String):Boolean;
var
  i : Integer;
begin
Result:=True;
 if Str<>'' then
  for i:=1 to Length(Str) do
   if  Str[i]<>Element then
   begin
      Result:= False;
      exit;
   end;
end;

更新
最后使用Barry Kelly建议并添加 inline 指令，性能显着提高。

UPDATE finally using the Barry Kelly Suggestion and adding the inline directive, the performance was significantly improved.

function AllElementsAreEqual(Const Element:Char;Str:String):Boolean;inline;
type
ArrayInt = Array of Integer;
var
  i    : Integer;
  Delta: Integer;
  List : ArrayInt;
  Test : Integer;
begin
  Result:=True;
  Delta:=(Length(Str) mod  4);
  if Delta<>0 then
  Str:=Str+StringOfChar(Element,4-Delta);
  Test:=Ord(Element) + Ord(Element) shl 8 + Ord(Element) shl 16 + Ord(Element) shl 24;
  List:=ArrayInt(@(Str[1]));

  for i:=0 to ((Length(Str) div 4)-1) do
   if List[i]<>Test  then
    begin
     Result:=False;
     exit;
    end;
end;

更新2

我很抱歉，但我发布了解决方案的旧实现（有一个bug），现在已经修复了。
感谢 The_Fox ，以更好地实施Barry建议。

i'm sorry but i posted an old implementation of the solution (with a bug), now is fixed. Thanks to The_Fox for create a better implementation of the Barry suggestion.

推荐答案

您可以考虑使用元素整数 c $ c>重复4次（因为这是Delphi 7中的 AnsiChar ），像 Ord（Element）+ Ord（Element）shl 8 + Ord（Element）shl 16 + Ord（Element）shl 24 ，然后将字符串转换为 PIntegerArray （ ^ array [0..MaxInt div 4 - 1] of Integer ）并循环它 Length（Str）div 4 times，以整数比较而不是人物。您需要手动比较最后几个 Length（str）mod 4 的字符。

You could consider creating an Integer value with the Element repeated 4 times (since this is AnsiChar in Delphi 7), shifted like Ord(Element) + Ord(Element) shl 8 + Ord(Element) shl 16 + Ord(Element) shl 24, then typecast the string to a PIntegerArray (^array[0..MaxInt div 4 - 1] of Integer) and loop over it Length(Str) div 4 times, comparing as integers instead of characters. You'll need to compare the last few Length(str) mod 4 characters manually though.

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