Workshop › 15 Puzzle › Step 12 of 27

Neighbours

What we are doing

Only a tile next to the gap can move. In the flat list the neighbours of i are i - N (above), i + N (below), i - 1 and i + 1, but only when they are on the board: position 3 ends a row, and 4 starts the next one.

```js
// The squares next to position i (up, down, left, right), staying inside the board.
function neighbors(i) {
  const list = []
  if (rowOf(i) > 0) list.push(i - N)
  if (rowOf(i) < N - 1) list.push(i + N)
  if (colOf(i) > 0) list.push(i - 1)
  if (colOf(i) < N - 1) list.push(i + 1)
  return list
}
```

What it means

• list starts empty; push adds a neighbour at the end.
• Each neighbour is added only when it exists: not in the top row for "above", not in the last column for "right"...
• return list gives the neighbours back.

Your turn

Under solvedTiles, leave an empty line and write the comment and neighbors. Press Run.

Skills: Arrays and objects

← The solved board from N Slide a tile →

All steps

1. A board in one list
2. The canvas and the pen
3. Paint the table
4. A function that draws
5. Row and column
6. Where each square is
7. Draw one tile
8. The number on the tile
9. All the tiles
10. Draw again and again
11. The solved board from N
12. Neighbours
13. Slide a tile
14. Click a tile
15. Arrow keys
16. Count the moves
17. Shuffle with real slides
18. Which boards can be solved?
19. Is it solved?
20. Remember the slide
21. Count the frames
22. Smooth sliding
23. Solved!
24. Show the win
25. Play again
26. A record to beat
27. Build it yourself: a timer