size_t size = board.size();

vector<int> row_counters(size, 0);

vector<int> col_counters(size, 0);

vector<int> box_counters(size, 0);

for (int r = 0; r < size; ++r)

{

for (int c = 0; c < size; ++c)

{

char digit_c = board[r][c];

if (digit_c != '.')

{

int digit = digit_c - '0';

int mask = 1 << digit;

size_t box_num = 3 * (r / 3) + c / 3;

if ((row_counters[r] & mask) || (col_counters[c] & mask) || (box_counters[box_num] & mask))

return false;

row_counters[r] |= mask;

col_counters[c] |= mask;

box_counters[box_num] |= mask;

}

}

}

return true;

for (int i = 0; i < 9; i++) {

for (int j = 0; j < 9; j++) {

for (int k = 0; k < 9; k++) {

}

}

}

return true;

}