Challenges

Two piles of matchsticks. Each turn you take as many as you like from one pile, and whoever takes the last match loses. Match the positions that are already lost for the player about to move.

You are given a string of 1s. Match it only when its length is a composite number — that is, not prime and not 1.

Eighty-one cells. Match the grid only when no digit repeats in any row, any column, or any 3×3 box.

A Sudoku box, flattened. Extract every digit that appears again later in the box.

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.

Squash every run of the same repeated character down to one of it.

Match any string containing the same word character twice in a row.

Match a well-formed hand: exactly five cards, single space separated, each a rank from A23456789TJQK followed by a suit from SHDC — and no card appearing twice. Hands are always sorted by rank, ascending.

Match text containing a quoted section — opened and closed by the same quote character, single or double.

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.

Match a noughts and crosses board that is a draw: every square filled, and neither player with three in a row.

Match text where the same word appears twice in a row.

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

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.