Prompt
• **Learn by Doing**
**Context:** I've set up the hint feature UI with a button that triggers the hint system. The infrastructure is ready: when clicked, it calls selectHintCell() to determine which cell to hint, then highlights that cell with a yellow background and shows possible values. The hint system needs to decide which empty cell would be most helpful to reveal to the user.
**Your Task:** In sudoku.js, implement the selectHintCell(board) function. Look for TODO(human). This function should analyze the board and return {row, col} for the best cell to hint, or null if the puzzle is complete.
**Guidance:** Consider multiple strategies: prioritize cells with only one possible value (naked singles), or cells that appear in rows/columns/boxes with many filled cells. You could also consider a balanced approach that helps without making it too easy. The board parameter is a 9x9 array where 0 represents empty cells.