[JAVA] sudoku en java

#include <cassert>
#include <iostream>
#include <string>
using namespace std;

bool rows[9][10], columns[9][10], squares[3][3][10];
string board[9];

bool solve(int k) {
    if (k == 9*9) return true;
    int r = k/9, c = k%9;
    for (char ch = '1'; ch <= '9'; ch++)
        if (board[r][c] == '*' || board[r][c] == ch ) {
            int digit = ch - '0';
            if (!rows[r][digit] && !columns[c][digit] && !squares[r/3][c/3][digit]) {
                rows[r][digit] = columns[c][digit] = squares[r/3][c/3][digit] = true;
                swap(board[r][c], ch);
                if (solve(k + 1)) return true;
                swap(board[r][c], ch);
                rows[r][digit] = columns[c][digit] = squares[r/3][c/3][digit] = false;
            }
        }
    return false;
}

int main() {
    for (int r = 0; r < 9; r++) cin >> board[r];
    assert(solve(0));
    for (int r = 0; r < 9; r++) cout << board[r] << endl;
}

$ cat sudoku.in 
*1*5*4**2
*3**7***6
7***9*8**
*639**127
***236***
492**568*
**7*8***4
1***2**9*
3**4*7*6*

$ ./solver < sudoku.in
918564372
235871946
746392815
563948127
871236459
492715683
627189534
154623798
389457261