Workshop › Puzzle Bobble-style Bubble Shooter › Step 16 of 31

Six neighbours

What we are doing

To find bubbles of the same color that touch, we need each cell's neighbours. In a honeycomb grid a cell has six: two beside it, two above and two below. Which columns those are depends on whether the row is shifted.

```js
const inGrid = (r, c) => r >= 0 && r < ROWS && c >= 0 && c < cols(r)

// The six cells around (r, c). Odd rows are shifted right, so their neighbours above and below are at c and c + 1;
// even rows' are at c - 1 and c.
function neighbors(r, c) {
  const shift = r % 2 === 0 ? -1 : 0
  return [
    [r, c - 1], [r, c + 1],
    [r - 1, c + shift], [r - 1, c + shift + 1],
    [r + 1, c + shift], [r + 1, c + shift + 1],
  ].filter(([nr, nc]) => inGrid(nr, nc))
}
```

What it means

inGrid checks that a row and column exist (odd rows have one cell less).
shift is -1 on even rows and 0 on odd rows; the cells above and below are at c + shift and c + shift + 1.
filter drops the neighbours that would be outside the grid.

Your turn

Above the cellPos line, write inGrid.
Under the cellPos line, write the comment and neighbors.

Skills: Arrays and objects

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