How to Implement a Timed Backtracking Algorithm for Sudoku Solver in Java?
I'm a bit lost with I'm working on a project and hit a roadblock... I'm trying to implement a backtracking algorithm to solve a Sudoku puzzle in Java, and I'm facing challenges with time constraints. My current implementation solves the puzzle correctly, but it sometimes takes too long for larger grids or more complex puzzles. I want to add a feature to limit the solving time to a specific duration (e.g., 2 seconds). If the algorithm exceeds this time limit, it should stop and return an indication that it couldn't solve the puzzle in time. Here's my existing code for the Sudoku solver using backtracking: ```java public class SudokuSolver { private static final int SIZE = 9; private static final int SUBGRIDSIZE = 3; public boolean solveSudoku(int[][] board) { for (int row = 0; row < SIZE; row++) { for (int col = 0; col < SIZE; col++) { if (board[row][col] == 0) { for (int num = 1; num <= SIZE; num++) { if (isValid(board, row, col, num)) { board[row][col] = num; if (solveSudoku(board)) { return true; } board[row][col] = 0; // backtrack } } return false; // no valid number found } } } return true; // puzzle solved } private boolean isValid(int[][] board, int row, int col, int num) { for (int i = 0; i < SIZE; i++) { if (board[row][i] == num || board[i][col] == num || board[row - row % SUBGRIDSIZE + i / SUBGRIDSIZE][col - col % SUBGRIDSIZE + i % SUBGRIDSIZE] == num) { return false; } } return true; } } ``` While this works for simpler Sudoku puzzles, when I run it on more complex examples, I sometimes hit the runtime limit, and the application freezes. To address this, I would like to implement a mechanism to interrupt the solving process after a certain time. I've considered using a separate thread to run the solving process, but I'm concerned about how to safely stop the thread without leaving the Sudoku board in an inconsistent state. Has anyone implemented a time-limited backtracking algorithm for Sudoku or something similar? Any advice or code snippets would be greatly appreciated! I'm using Java 11 and running this in a standard console application. I've also looked into the `ExecutorService` for managing threads, but I am not sure how to integrate this into my existing code effectively. My development environment is Linux. Has anyone else encountered this? Any suggestions would be helpful.