| Regular Expressions |
Article Index for Regular |
Website Links For Regular |
Information AboutRegular Expressions |
| CATEGORIES ABOUT REGULAR EXPRESSION | |
| formal languages | |
| pattern matching | |
| programming language topics | |
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BASIC CONCEPTS | |||
| (''concatenation'') ''RS'' Denoting The Set { αβ α In ''R'' And β In ''S'' } For Example {"ab", "c"}{"d", "ef"} | {"abd", "abef", "cd", "cef"} |
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| The Formal Definition Of Regular Expressions Is Purposely Parsimonious And Avoids Defining The Redundant Quantifiers And +, Which Can Be Expressed As Follows: ''a''<sup>+</sup> | aa, and ''a'' = (εa) Sometimes the complement operator ~ is added ~''R'' denotes the set of all strings over Σ that are not in ''R'' The complement operator is redundant: it can always be expressed by only using the other operators |
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| { Valign | "top" |
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| { Class | "wikitable" |
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| :"( | "cC" class="copylinks" target="_blank">{Link without Title} at)( {Link without Title} og)" matches "cat", "Cat", "dog" and "Dog" |
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| The Other Algorithm Is To Match The Pattern Against The Input String By | "http://wwwinformationdelightinfo/encyclopedia/entry/backtracking" class="copylinks">Backtracking (This algorithm is sometimes called NFA, but this terminology is highly confusing) Its running time can be exponential, which simple implementations exhibit when matching against expressions like "(aaa)b" that contain both alternation and unbounded quantification and force the algorithm to consider an exponential number of subcases More complex implementations identify and speed up various common cases where they would otherwise run slowly |
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