Custom-Regexp-Engine

A custom regular expression engine that takes into account the carriage position when searching for a substring that satisfies a regular expression.

Specification:

• You have to use a backslash (\) as an escape character before the characters \, ?, *, +, (, and ). For instance, use \\ when you want a backslash, and \? for a question mark, etc.
• All other characters are read literally.
• There's a \c character that specifies the caret position. This means that the w\cord pattern looks for instances of 'word' where the caret is positioned between w and o.
• Similar to the majority of existing patterns, any content in brackets is a group. A group supports the quantifiers ?, *, and +, where:
  • ? denotes 0 or 1 repetition.
  • * denotes 0 or more repetitions.
  • + denotes 1 or more repetitions.
  • Quantifiers can only be placed after the closing bracket of a group.
• A group must have content. It cannot be empty.
• Regular expressions should work using only ASCII characters. Other characters are not allowed.

Examples

Input text	Caret position	Pattern	Result
Hello world!	Doesn't matter	word	[[6, 11]]
Hello world!	Doesn't matter	Hello( word\!)?	[[0, 5], [0, 12]]
Ho-ho-ho	Doesn't matter	Ho(-ho)*	[[0, 2], [0, 5], [0, 8]]
word word word	Caret with offset == 3	\cword	[]
word word word	Caret with offset == 5	\cword	[[5, 9]]
word word word	Caret with offset == 0, caret with offset == 5	\cword	[[0, 4], [5, 9]]