68 challenges across eight tiers. Tier 8 is a warm-up; tier 1 will take an evening. Nothing is locked — play them in any order.
Match a valid IPv4 address — four numbers 0 to 255, separated by dots, and nothing else.
The boss. Is the black king attacked by anything at all — pawn, knight, bishop, rook, queen or the white king?
A hand is five cards as "2H 3S 4D 5C 6H" — rank then suit, space separated, and always sorted by rank, ascending. The rank ladder is A 2 3 4 5 6 7 8 9 T J Q K: the ace is low, so A-2-3-4-5 is a run and A-T-J-Q-K is not. Match a hand whose five ranks are consecutive on that ladder.
Does a white knight attack the black king? Eight fixed jumps, and nothing can block a knight.
Match strings containing "cat" or "dog" as a whole word.
Extract the fields of a CSV row, where a quoted field may contain commas. Quoted fields keep their quotes.