What are some potential pitfalls when using backtracking and recursion in PHP to solve Sudoku fields automatically?

One potential pitfall when using backtracking and recursion in PHP to solve Sudoku fields automatically is the possibility of infinite recursion if the algorithm gets stuck in a loop. To prevent this, it's important to include a base case that stops the recursion when a solution is found or when no valid moves are left. Additionally, keeping track of the current state of the Sudoku board and undoing moves when necessary can help avoid errors. 

function solveSudoku(&$board) {
    // Base case: check if the board is solved
    if (boardIsSolved($board)) {
        return true;
    }
    
    // Find an empty cell to fill
    $emptyCell = findEmptyCell($board);
    
    // Try filling the empty cell with valid numbers
    for ($num = 1; $num <= 9; $num++) {
        if (isValidMove($board, $emptyCell, $num)) {
            $board[$emptyCell['row']][$emptyCell['col']] = $num;
            
            // Recursively solve the rest of the board
            if (solveSudoku($board)) {
                return true;
            }
            
            // Undo the move if it didn't lead to a solution
            $board[$emptyCell['row']][$emptyCell['col']] = 0;
        }
    }
    
    // No valid move found, backtrack
    return false;
}

Keywords

backtracking recursion Sudoku PHP pitfalls

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