题解 | #Sudoku# 学习解题思路

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws IOException {
        // 创建一个9x9的二维数组来表示数独盘面
        int[][] board = new int[9][9];
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

        // 逐行读取用户输入的数独盘面
        for (int i = 0; i < 9; i++) {
            String[] row = reader.readLine().split(" ");
            for (int j = 0; j < 9; j++) {
                board[i][j] = Integer.parseInt(row[j]);
            }
        }

        // 调用方法解决数独
        solveSudoku(board);

        // 打印解决后的数独盘面
        printBoard(board);
    }

    // 解决数独的方法
    public static void solveSudoku(int[][] board) {
        solve(board);
    }

    // 递归求解数独
    public static boolean solve(int[][] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                // 如果当前格子为空
                if (board[i][j] == 0) {
                    for (int num = 1; num <= 9; num++) {
                        if (isValid(board, i, j, num)) {
                            board[i][j] = num;
                            if (solve(board)) {
                                return true;
                            } else {
                                board[i][j] = 0;
                            }
                        }
                    }
                    return false;
                }
            }
        }
        return true;
    }

    // 检查数字在当前位置是否有效
    public static boolean isValid(int[][] board, int row, int col, int num) {
        for (int i = 0; i < 9; i++) {
            if (board[row][i] == num || board[i][col] == num ||
                    board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == num) {
                return false;
            }
        }
        return true;
    }

    // 打印数独盘面
    public static void printBoard(int[][] board) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                System.out.print(board[i][j] + " ");
            }
            System.out.println();
        }
    }
}