循环:
var pattern = _dict[key];
string before;
do
{
before = pattern;
foreach (var pair in _dict)
if (key != pair.Key)
pattern = pattern.Replace(string.Concat("{", pair.Key, "}"), string.Concat("(", pair.Value, ")"));
} while (pattern != before);
return pattern;
它只是在一堆键上重复查找和替换。字典就是<string,string> .
我可以看到对此有 2 处改进。
- 每次我们做
pattern.Replace它再次从字符串的开头搜索。如果它打到第一个会更好{，它只会查找匹配项的键列表(可能使用二进制搜索)，然后替换适当的键。 pattern != beforebit 是我检查迭代期间是否有任何东西被替换的方式。如果pattern.Replace函数返回了多少或是否实际发生了任何替换，我不需要这个。
但是......我真的不想写一个大的讨厌的东西类来做所有这些。这一定是一个相当普遍的场景？有没有现成的解决方案？
全类
感谢 Elian Ebbing 和 ChrisWue。
class FlexDict : IEnumerable<KeyValuePair<string,string>>
{
private Dictionary<string, string> _dict = new Dictionary<string, string>();
private static readonly Regex _re = new Regex(@"{([_a-z][_a-z0-9-]*)}", RegexOptions.Compiled | RegexOptions.IgnoreCase);
public void Add(string key, string pattern)
{
_dict[key] = pattern;
}
public string Expand(string pattern)
{
pattern = _re.Replace(pattern, match =>
{
string key = match.Groups[1].Value;
if (_dict.ContainsKey(key))
return "(" + Expand(_dict[key]) + ")";
return match.Value;
});
return pattern;
}
public string this[string key]
{
get { return Expand(_dict[key]); }
}
public IEnumerator<KeyValuePair<string, string>> GetEnumerator()
{
foreach (var p in _dict)
yield return new KeyValuePair<string,string>(p.Key, this[p.Key]);
}
IEnumerator IEnumerable.GetEnumerator()
{
return GetEnumerator();
}
}
示例用法
class Program
{
static void Main(string[] args)
{
var flex = new FlexDict
{
{"h", @"[0-9a-f]"},
{"nonascii", @"[\200-\377]"},
{"unicode", @"\\{h}{1,6}(\r\n|[ \t\r\n\f])?"},
{"escape", @"{unicode}|\\[^\r\n\f0-9a-f]"},
{"nmstart", @"[_a-z]|{nonascii}|{escape}"},
{"nmchar", @"[_a-z0-9-]|{nonascii}|{escape}"},
{"string1", @"""([^\n\r\f\\""]|\\{nl}|{escape})*"""},
{"string2", @"'([^\n\r\f\\']|\\{nl}|{escape})*'"},
{"badstring1", @"""([^\n\r\f\\""]|\\{nl}|{escape})*\\?"},
{"badstring2", @"'([^\n\r\f\\']|\\{nl}|{escape})*\\?"},
{"badcomment1", @"/\*[^*]*\*+([^/*][^*]*\*+)*"},
{"badcomment2", @"/\*[^*]*(\*+[^/*][^*]*)*"},
{"baduri1", @"url\({w}([!#$%&*-\[\]-~]|{nonascii}|{escape})*{w}"},
{"baduri2", @"url\({w}{string}{w}"},
{"baduri3", @"url\({w}{badstring}"},
{"comment", @"/\*[^*]*\*+([^/*][^*]*\*+)*/"},
{"ident", @"-?{nmstart}{nmchar}*"},
{"name", @"{nmchar}+"},
{"num", @"[0-9]+|[0-9]*\.[0-9]+"},
{"string", @"{string1}|{string2}"},
{"badstring", @"{badstring1}|{badstring2}"},
{"badcomment", @"{badcomment1}|{badcomment2}"},
{"baduri", @"{baduri1}|{baduri2}|{baduri3}"},
{"url", @"([!#$%&*-~]|{nonascii}|{escape})*"},
{"s", @"[ \t\r\n\f]+"},
{"w", @"{s}?"},
{"nl", @"\n|\r\n|\r|\f"},
{"A", @"a|\\0{0,4}(41|61)(\r\n|[ \t\r\n\f])?"},
{"C", @"c|\\0{0,4}(43|63)(\r\n|[ \t\r\n\f])?"},
{"D", @"d|\\0{0,4}(44|64)(\r\n|[ \t\r\n\f])?"},
{"E", @"e|\\0{0,4}(45|65)(\r\n|[ \t\r\n\f])?"},
{"G", @"g|\\0{0,4}(47|67)(\r\n|[ \t\r\n\f])?|\\g"},
{"H", @"h|\\0{0,4}(48|68)(\r\n|[ \t\r\n\f])?|\\h"},
{"I", @"i|\\0{0,4}(49|69)(\r\n|[ \t\r\n\f])?|\\i"},
{"K", @"k|\\0{0,4}(4b|6b)(\r\n|[ \t\r\n\f])?|\\k"},
{"L", @"l|\\0{0,4}(4c|6c)(\r\n|[ \t\r\n\f])?|\\l"},
{"M", @"m|\\0{0,4}(4d|6d)(\r\n|[ \t\r\n\f])?|\\m"},
{"N", @"n|\\0{0,4}(4e|6e)(\r\n|[ \t\r\n\f])?|\\n"},
{"O", @"o|\\0{0,4}(4f|6f)(\r\n|[ \t\r\n\f])?|\\o"},
{"P", @"p|\\0{0,4}(50|70)(\r\n|[ \t\r\n\f])?|\\p"},
{"R", @"r|\\0{0,4}(52|72)(\r\n|[ \t\r\n\f])?|\\r"},
{"S", @"s|\\0{0,4}(53|73)(\r\n|[ \t\r\n\f])?|\\s"},
{"T", @"t|\\0{0,4}(54|74)(\r\n|[ \t\r\n\f])?|\\t"},
{"U", @"u|\\0{0,4}(55|75)(\r\n|[ \t\r\n\f])?|\\u"},
{"X", @"x|\\0{0,4}(58|78)(\r\n|[ \t\r\n\f])?|\\x"},
{"Z", @"z|\\0{0,4}(5a|7a)(\r\n|[ \t\r\n\f])?|\\z"},
{"Z", @"z|\\0{0,4}(5a|7a)(\r\n|[ \t\r\n\f])?|\\z"},
{"CDO", @"<!--"},
{"CDC", @"-->"},
{"INCLUDES", @"~="},
{"DASHMATCH", @"\|="},
{"STRING", @"{string}"},
{"BAD_STRING", @"{badstring}"},
{"IDENT", @"{ident}"},
{"HASH", @"#{name}"},
{"IMPORT_SYM", @"@{I}{M}{P}{O}{R}{T}"},
{"PAGE_SYM", @"@{P}{A}{G}{E}"},
{"MEDIA_SYM", @"@{M}{E}{D}{I}{A}"},
{"CHARSET_SYM", @"@charset\b"},
{"IMPORTANT_SYM", @"!({w}|{comment})*{I}{M}{P}{O}{R}{T}{A}{N}{T}"},
{"EMS", @"{num}{E}{M}"},
{"EXS", @"{num}{E}{X}"},
{"LENGTH", @"{num}({P}{X}|{C}{M}|{M}{M}|{I}{N}|{P}{T}|{P}{C})"},
{"ANGLE", @"{num}({D}{E}{G}|{R}{A}{D}|{G}{R}{A}{D})"},
{"TIME", @"{num}({M}{S}|{S})"},
{"PERCENTAGE", @"{num}%"},
{"NUMBER", @"{num}"},
{"URI", @"{U}{R}{L}\({w}{string}{w}\)|{U}{R}{L}\({w}{url}{w}\)"},
{"BAD_URI", @"{baduri}"},
{"FUNCTION", @"{ident}\("},
};
var testStrings = new[] { @"""str""", @"'str'", "5", "5.", "5.0", "a", "alpha", "url(hello)",
"url(\"hello\")", "url(\"blah)", @"\g", @"/*comment*/", @"/**/", @"<!--", @"-->", @"~=",
"|=", @"#hash", "@import", "@page", "@media", "@charset", "!/*iehack*/important"};
foreach (var pair in flex)
{
Console.WriteLine("{0}\n\t{1}\n", pair.Key, pair.Value);
}
var sw = Stopwatch.StartNew();
foreach (var str in testStrings)
{
Console.WriteLine("{0} matches: ", str);
foreach (var pair in flex)
{
if (Regex.IsMatch(str, "^(" + pair.Value + ")$", RegexOptions.IgnoreCase | RegexOptions.ExplicitCapture))
Console.WriteLine(" {0}", pair.Key);
}
}
Console.WriteLine("\nRan in {0} ms", sw.ElapsedMilliseconds);
Console.ReadLine();
}
}
目的
用于构建可以相互扩展的复杂正则表达式。也就是说，我正在尝试实现 the css spec .
最佳答案
我认为如果您使用正则表达式查找任何出现的 {foo} 会更快，然后使用 MatchEvaluator如果 foo 恰好是字典中的键，则替换 {foo}。
目前我这里没有 visual studio，但我想这在功能上等同于您的代码示例:
var pattern = _dict[key];
bool isChanged = false;
do
{
isChanged = false;
pattern = Regex.Replace(pattern, "{([^}]+)}", match => {
string matchKey = match.Groups[1].Value;
if (matchKey != key && _dict.ContainsKey(matchKey))
{
isChanged = true;
return "(" + _dict[matchKey] + ")";
}
return match.Value;
});
} while (isChanged);
请问您为什么需要 do/while 循环？字典中键的值是否可以再次包含必须替换的 {placeholders}？你能确定你不会陷入无限循环吗，其中键 "A" 包含 "Blahblah {B}" 和键 "B" 包含 "Blahblah {A}"？
编辑:进一步的改进是:
- 使用预编译的正则表达式。
- 使用递归而不是循环(参见 ChrisWue's 评论)。
- 使用
_dict.TryGetValue()，如 Guffa's代码。
你最终会得到一个 O(n) 算法，其中 n 是输出的大小，所以你不能做得比这更好。
关于c# - 我怎样才能加快这个循环？是否有一次替换多个术语的类？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5364309/