Four Pieces Strategy: Strong Squares, Forks and the AI Levels

Updated October 2026

Four Pieces fits a whole strategy game into a 5×5 board and eight pieces. You and the computer each place four pieces, then take turns sliding them, and the first to arrange all four in a straight line or a tight square wins. With so few pieces, every placement matters, and the computer opponent changes character as your streak grows. This guide explains how the game scores the board, how the opponent thinks at each stage, and how to build wins rather than wait for them.

The rules as this version plays them

Play has two phases. In the drop phase, the two sides alternate placing a piece on any empty square until each has four on the board. In the move phase, a turn means sliding one of your own pieces one step to an empty neighbouring square in any of the eight directions, diagonals included. Nothing is ever captured or jumped.

A shape counts the instant it appears, even during the drop phase. There are 44 winning shapes in total: 10 horizontal lines, 10 vertical lines, 8 diagonals and 16 two-by-two squares. Squares make up more than a third of the list, which is why they catch so many players off guard.

A round can also be drawn. Once the move phase has run for 60 slides between the two sides, the round is declared a draw, and it is also drawn if the side to move has no legal slide. A draw ends your run just like a loss. You move first in the opening round, and the first move then alternates every round, so half of your rounds start with the computer dropping first.

Which squares are worth the most

Count how many of the 44 shapes run through each square and a clear map appears. The centre is in 12 shapes. The eight squares around it are in 10 each. Then there is a drop-off: the squares next to the corners along the edges are in 6, the middle of each edge is in only 5, and the corners are in just 4.

Two things stand out. The inner three-by-three block holds almost all the value, and the edge midpoints are slightly worse than the squares beside them, because they sit on no diagonal at all. A piece on an edge midpoint is mostly a blocker. The computer adds this same count into its own evaluation, so expect it to grab the centre and inner ring whenever it has nothing more urgent to do.

How the opponent changes with your streak

The computer has four settings, chosen by your current streak:

• Streak 0–1: a short two-move lookahead, but half of its moves are picked completely at random.
• Streak 2–4: the same lookahead with a random move about one time in five (22 percent).
• Streak 5–9: a deeper four-move lookahead with random moves 15 percent of the time.
• Streak 10 and up: the four-move lookahead and no random moves.

Even without randomness it is not unbeatable. When several moves look equally good it picks among them at random, and its judgement of quiet positions comes from a simple score: pieces on valuable squares, shapes that are still open, and how many squares would complete a shape for each side. It values having two such finishing squares far more than one, so it does understand forks, but it only sees four moves ahead. In our simulation, a plain two-move search playing against the top setting won 8 of 40 rounds, lost 14 and drew 18. Draws are common at the top level, and since a draw ends the run, every round there has to be won outright.

Winning the drop phase

Most rounds are decided before anyone slides. Four pieces are enough to win outright during the drop, so the first job is defensive: whenever the computer has three pieces on one open shape, the fourth square must be taken immediately. Check squares as carefully as lines; three pieces in an L shape are one drop away from a square.

The attacking goal is a fork, two separate shapes that each need one more piece. The computer can only fill one empty square per turn, so a genuine fork wins. A compact cluster in the inner ring is the easiest way to get one, because a two-by-two square and a line share pieces there. The simplest fork of all is three pieces in a row through the centre: a five-square row contains two four-square lines, so three in the middle can be finished at either end, and one block cannot stop both.

When the computer drops first, take the centre if it is still free. When you drop first, the centre is the natural opening; your second piece should go next to it on the inner ring, where it adds to as many shapes as possible.

Playing the move phase

Once all eight pieces are down, think in terms of distance. A shape is only a threat if a piece can slide into the missing square in one move, and the square must still be empty when that happens. Before sliding, check two things: which square you are emptying, and whether that empty square finishes a shape for the opponent. Many losses come from a piece walking away from a square it was quietly blocking.

Diagonal slides are where human players lose track. A piece can reach any of up to eight neighbours, so a corner of a square can be filled from directly beside it or from a diagonal. When you count how many of the opponent's pieces can reach a key square, count all eight directions.

A useful technique is the waiting slide: moving a piece that is not doing any blocking work, so the position keeps its shape and the opponent has to commit. The 60-slide limit means you cannot shuffle forever — reaching it is a draw, which ends your run — but early in the move phase, making a harmless move and letting the computer weaken its own structure is often the strongest plan.

Managing a streak

Your streak climbs by one per win and is lost on a single defeat or draw, at which point the run ends and the final streak can be submitted to the Hall of Fame. The New button behaves differently mid-run: if your streak is above zero, pressing it ends the run on the spot and shows the game-over card, rather than wiping your score silently.

Because a draw ends the run, a locked-up level position is not a safe result: you need a win before the slide limit. Use the early move phase to manoeuvre towards a fork while the board is still fluid, and keep your risk for positions where you can count a real fork rather than gambling at the last slides. Your best streak is stored on this device, and the board deals a fresh round about a second after each win.