题解 | #Sudoku#

public class Main {
    static int[][] arr = new int[9][9];
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                arr[i][j] = scanner.nextInt();
            }
        }
        recursion();
        for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                System.out.print(arr[i][j] + " ");
            }
            System.out.println();
        }
    }
    
    static boolean recursion() {
        int row = 9, col = 9;
        out : for (int i = 0; i < 9; i++) {
            for (int j = 0; j < 9; j++) {
                if (arr[i][j] == 0) {
                    row = i;
                    col = j;
                    break out;
                }
            }
        }
        if (row == 9) {
            return true;
        }
        for (int i = 0; i < 9; i++) {
            if (isValid(row, col, i + 1)) {
                arr[row][col] = i + 1;
                if (recursion()) {
                    return true;
                }
            }
        }
        arr[row][col] = 0;
        return false;
    }
    
    static boolean isValid(int row, int col, int val) {
        for (int i = 0; i < 9; i++) {
            if (arr[row][i] == val) {
                return false;
            }
        }
        for (int i = 0; i < 9; i++) {
            if (arr[i][col] == val) {
                return false;
            }
        }
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                if (arr[row / 3 * 3 + i][col / 3 * 3 + j] == val) {
                    return false;
                }
            }
        }
        return true;
    }
}