Slalom techniques

Slalom puzzles look open at first. Most of the work is noticing how little room the gates and black squares really leave. These are the moves you’ll use on every puzzle.

In each picture, the cells the technique decides are outlined in blue.

1. Straight through the gate

   The loop crosses a gate at a right angle. So a one-square gate between two black squares fixes three squares at once: the gate square and the squares on either side of it, in a straight line.

2. One crossing per gate

   Each gate is passed exactly once. As soon as you know where the loop crosses a long gate, every other square of that gate is off-limits.

3. Dead ends stay empty

   Every square on the loop needs two open sides, one way in and one way out. A square boxed in so that only one side is open can never be used.

4. Corners make the loop turn

   A loop through a corner square has to turn there, because only two of its sides are open. The same goes for any square walled in on two neighboring sides by black squares or the edge.

5. Count from the circle

   Numbers fix the order. Leaving the circle one way or the other, the first gate you reach must be gate 1. Here only the left way reaches gate 1 before any other gate, so that’s the way the loop sets off.

When you’re stuck, pick a gate and ask where the loop could possibly cross it. Squares it can’t reach, and squares that would need a third line, rule out more of the board than you’d expect.