Corner Control and Entry Line Design

Corners are force multipliers. A robot parked at the right corner can support two or more future turns.

Do not spend corner positions on temporary ideas unless they unlock immediate value.

On the 16x16 board, the four board corners (1,1), (1,16), (16,1), and (16,16) are special because any robot pushed there is guaranteed to stop. This makes them zero-cost parking spots: you never waste a move on a robot that accidentally slides past a corner. But the truly valuable corners are the internal ones created by L-shaped wall segments. A robot parked next to an L-wall can block movement in two perpendicular directions, making it a dual-purpose stopper.

Map the high-value corners at the start of each puzzle. Look for wall configurations that form natural pockets where a robot can sit and influence two lanes simultaneously. These positions are worth investing a setup move to reach.

Avoid polluting your target entry line with random helper placements. Keep one side clean for guaranteed final slide.

An entry line is the row or column through which your target robot will make its final approach to the goal. If the target needs to slide right along row 8 to reach (8, 11), then row 8 from the target robot's column to column 11 is your entry line. Any robot accidentally placed in that stretch will either need to be moved (wasting a move) or will create an unintended stop.

Before placing any helper robot, ask: does this placement cross my planned entry line? If the answer is yes, either find an alternative stopper position or ensure the helper robot is part of the intended stopping chain. Discipline about entry lines separates intermediate players from beginners more than any other single skill.

Walls on the 16x16 board come in two varieties: straight walls (blocking one side of a cell) and L-shaped walls (blocking two adjacent sides of a cell). L-walls create natural corner pockets that are extremely useful for routing.

When scanning the board, look for L-walls near the target. An L-wall one or two cells away from the target often defines the best approach direction. If the target is at (7, 9) and there is an L-wall at (7, 10) blocking the right and bottom sides, then approaching from the left along row 7 is likely the intended path because the wall at (7, 10) provides a natural stop.

Straight walls are simpler but still important. A straight wall on the bottom of (5, 9) means any robot sliding down column 9 will stop at row 5. Map these stops quickly and use them as anchoring points for your route.

If an entry line is blocked, do not brute force. Rebuild from nearest corner and reroute with one support robot.

A common scenario: you planned to send red right along row 6 to the target, but you just moved blue into row 6 as a stopper for a different purpose. Now red cannot slide cleanly. Instead of undoing everything, scan for alternative entry. Maybe red can approach from column direction instead, sliding down to reach the target from above. The L-wall that made the row approach attractive might also support a column approach with a minor helper adjustment.

Flexibility is key. The best players maintain two or three candidate entry lines in mind simultaneously. When one gets blocked, they smoothly switch to the next option without losing composure or time.

In complex puzzles, corner positions chain together. Robot A sits in corner position X, which stops robot B at position Y, which in turn stops the target at the goal. This chain of corner-based stops is often the backbone of 4- and 5-move solutions.

To spot chain opportunities, trace backward from the target through wall corners. If the target needs to stop at (8, 11) and there is a wall corner at (8, 12), then something must deliver the target into row 8. If (5, 11) has a wall corner, a robot parked there could stop the target at row 5 on column 11 before a horizontal push along row 5. Each corner becomes a waypoint in a multi-step route.

Practice this by studying solved puzzles and mapping which wall corners were used in the solution. Over time you will develop an intuition for which corners are load-bearing and which are decorative on any given board.