void wpisywanieSudokuDoRozwiazania(){
    int a;
for (int j=0;j<21;j++){
    for (int i=0;i<9;i++){
        cin >> a;
        sudoku[j][i]=a;
    }
}
}

bool solve(int x, int y);

int sudoku[9][9] = { /* tu zadane sudoku... */ };
int curr[9][9];
bool can_insert(int x, int y, int value) {
    for(int i = 0; i < 9; i++) {
        if (value == curr[x][i] || value == curr[i][y] ||
            value == curr[x/3*3+i%3][y/3*3+i/3]) return false;
    } return true;
}

bool next(int x, int y) {
    if (x == 8 && y == 8) return true;
    else if (x == 8) return solve(0, y + 1);
    else return solve(x + 1, y);
}

bool solve(int x, int y) {
    if (sudoku[x][y] == 0) {
        for(int i = 1; i <= 9; i++) {
            if (can_insert(x, y, i)) {
                curr[x][y] = i;
                if (next(x, y)) return true;
            }
        } curr[x][y] = 0; return false;
    } return next(x, y);
}