Ice sliding puzzles feel unfair for about a minute. You slide, you land somewhere you didn't want, and your plan falls apart. The way out is to stop thinking forwards. Here's a small board, and how to solve it from the hole backwards.
The board
This is a 5 by 5 board like the first one in Glide. The ball starts at @, the hole is O, and # is a rock. Squares are numbered by column and then row, so (1,2) is the left edge, second row down.
. . . . # @ . . # . . . . . # . . # . O # # . . .
The ball slides until a rock or the edge stops it. The hole stops it too, so any slide that passes over the hole ends in it. The shortest route here is 6 moves.
Step 1: ask which stops reach the hole
Look at the hole at (5,4). What can slide into it?
- From the left along row 4: the rock at (3,4) is in the way, and (4,4) isn't a place you can stop. So that's out.
- From above in column 5: there's a rock at (5,3). Out.
- From below: a ball at (5,5) sliding up passes straight into the hole. In.
Only one stop works: (5,5).
Step 2: ask how to reach that stop
You can stop at (5,5) by sliding right along the bottom row, because the edge stops you. Which stops are on that row? You can reach (4,5), and from there a slide right ends at (5,5).
Step 3: keep going
How do you reach (4,5)? Slide down column 4 from (4,3). The bottom edge stops you at (4,5), and you pass the square next to the hole on the way. (4,3) is a stop because the rock at (5,3) halts a slide right along row 3.
And (4,3) comes from sliding right along row 3 from (3,3). (3,3) comes from sliding down column 3 from (3,2), because the rock at (3,4) stops you. And (3,2) is one slide right from the start, where the rock at (4,2) stops you.
Read it forwards and that's the route:
- Right, to (3,2)
- Down, to (3,3)
- Right, to (4,3)
- Down, to (4,5)
- Right, to (5,5)
- Up, into the hole at (5,4)
Six moves, which is the shortest possible. Working backwards, every step had only a choice or two, so there was almost nothing to search.
What the wrong first moves cost you
The hole is to the right and down, so the obvious first move is down. Try it and the ball slides to (1,4), where the rock at (1,5) stops it. That's a dead end. From (1,4) you can only reach (1,1), (2,1), (2,4) and (4,1), and from any of them you can only reach the others. The hole is out of reach forever. Sliding up from the start has the same problem, because it lands you at (1,1) in the same group.
In Glide, getting out of a dead end means Undo or Reset, and both cost moves. That's why a slide made "just to see" isn't free.
What is a decoy stop?
A decoy looks like progress but isn't. Here (4,3) shows how it happens: it's only two squares from the hole, yet three slides away. It happens to be on the route this time. On Glide's 7 by 7 and 9 by 9 boards, the game builds stops like that which sit close to the hole but cost many moves, and it steers away from boards where simply heading toward the hole works.
Tips to take with you
- Work backwards. Find the stops that slide into the hole, then the stops that reach those.
- Count slides, not squares. A stop that's close on the map can be far in moves.
- Plan before your first move. On a 9 by 9 board it's worth a few seconds to find the end of the route first.
- Walls count. The edges stop you as well as rocks. Many routes run along the outside.
- Don't scout with Undo. In Glide it costs a move.
Want the full rules? Read how to play Glide. If you like this kind of puzzle, see ice sliding puzzles for more.