Five in a Row is the pencil-and-paper game of noughts and crosses grown up: a 15×15 board and a line of five to make. It is fast to learn and quick to play, and the computer at Master searches forcing sequences of fours before every move.
Rules
Players take turns placing one stone on any empty intersection of the 15×15 grid. Dark places the first stone. Stones never move and are never removed.
The first player to make an unbroken line of five stones of their colour, horizontally, vertically or diagonally, wins. In the five or more variant a line of six or longer also wins; in the exactly five variant an overline of six or more does not count.
If the board fills up with no winning line, the game is a draw, although between players of any strength that is rare.
Strategy
Know your threats. An open three is three in a row with both ends free: if it is not answered it becomes an open four, which cannot be stopped because it wins at either end. A four with one end blocked must be answered at once.
Win with forcing moves. A sequence where every move makes a four leaves the opponent no choice: they must block each one. If the last four arrives with a second threat, it wins. The puzzles train exactly this.
Defend early. Answer an open three before it becomes a four, and prefer blocks that also extend your own lines. Waiting one move too long usually loses.
Play close. Stones far from the action do almost nothing. Most good moves are within two intersections of the existing stones, and moves that join two of your groups are worth looking at first.
Questions
Is this the same as gomoku?
It is the free-style family of five-in-a-row games. There are no opening restrictions here, so the first player has an advantage on an empty board.
What is the difference between the two variants?
In 'five or more' any line of at least five wins. In 'exactly five' a line of six or more is an overline and does not win, which changes some attacking shapes.
Why does the computer sometimes answer instantly?
A forced reply, like stopping a four, needs no search, so it comes at once. Before any normal search the computer also looks for a forced win of its own.
Can I undo a move?
Yes. Undo takes back your last move and the computer's reply; in a game for two players it takes back one move.
How big is the board?
Fifteen by fifteen intersections, labelled a to o and 1 to 15 for the move list.