题解 | Sudoku

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        //棋盘
        int[][] grid = new int[9][9];
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                grid[i][j] = scanner.nextInt();
            }
        }
        fillSudoku(grid);
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 8; j++) {
                System.out.print(grid[i][j] + " ");
            }
            System.out.println(grid[i][8]);//每行的最后一个数字换行
        }
    }

    public static boolean fillSudoku(int[][] grid) {
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (grid[i][j] != 0) continue;
                for (int k = 1; k <= 9; k++) {
                    if (isNumValid(grid, i, j, k)) {
                        //把k放到当前位置
                        grid[i][j] = k;
                        if(fillSudoku(grid)){
                            return true;
                        }
                        grid[i][j] = 0;
                    }
                }
                //9个数都试玩了，都不行
                return false;
            }
        }
        return true;
    }

    public static boolean isNumValid(int[][] grid, int i, int j, int val) {
        //横向判断
        for (int k = 0; k < 9; k++) {
            if (grid[i][k] == val && k != j) {
                return false;
            }
        }
        //纵向判断
        for (int m = 0; m < 9; m++) {
            if (grid[m][j] == val && m != i) {
                return false;
            }
        }

        //九宫格判断
        int startRow = (i / 3) * 3, startCol = (j / 3) * 3;
        for (int y = startRow; y < startRow + 3; y++) {
            for (int z = startCol; z < startCol + 3; z++) {
                if (y != i && z != j && grid[y][z] == val) {
                    return false;
                }
            }
        }
        return true;
    }
}