Workshop › Sudoku › Step 18 of 28

The easiest cell

What we are doing

Now we teach the computer to solve. A human starts with the cell where the fewest digits fit, and so will the computer: bestCell finds the empty cell with the fewest options, and lists them.

```js
// The empty cell with the fewest digits that fit, and those digits.
function bestCell(board) {
  let found = null
  for (let r = 0; r < 9; r++) {
    for (let c = 0; c < 9; c++) {
      if (board[r][c] !== 0) continue
      const options = []
      for (let d = 1; d <= 9; d++) if (canPlace(board, r, c, d)) options.push(d)
      if (!found || options.length < found.options.length) found = { r, c, options }
    }
  }
  return found
}
```

What it means

For every empty cell, options lists the digits that fit, using canPlace.
found keeps the cell with the shortest list so far.
On a full board there is no empty cell, and the answer is null.

Your turn

Under canPlace, write the comment and bestCell.

Skills: Loops, Arrays and objects

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