Challenges

The same 7x6 Connect Four board, but now a win counts in any direction — across, down, or either diagonal. Capture the winning colour, or nothing.

A hand is five cards as "AS 7H 7D 9C KS" — rank then suit, space separated, and always sorted by rank, ascending. Capture the rank that appears more than once, or match nothing if every rank is different.

Capture the major, minor and patch numbers of a version, plus its prerelease tag — or nothing in group 4 when there is no prerelease.

A Sudoku row is nine characters. Capture the digit that appears twice — and match nothing at all when the row is legal.

A Connect Four board, 7 wide and 6 tall, arrives as one flat string. Capture the colour — R or Y — that has four in a row horizontally. Capture nothing if neither has.

A hand is five cards as "AS 2H 5D 9C KS" — rank then suit, space separated. Ranks are A23456789TJQK (T is ten), suits are SHDC. Capture the suit if all five cards share one; no match if they do not.

A white pawn checks the black king from the square down-left or down-right of it. Capture both squares.

Capture the year, month and day of an ISO date as three separate groups.

Capture the key and the value from a "key = value" line, whatever the spacing.

Pull the timestamp, the level and the message out of a bracketed log line.

Capture everything before the FIRST equals sign: key=value=other gives key.

Capture everything between the opening and closing --- markers of a Markdown front-matter block.

Capture the file extension of a filename: report.q3.pdf gives pdf, not q3.pdf.