36.cpp

#include <iostream>
using namespace std;

const int Row_size = 9, Column_size = 9;

bool check_row(const vector<vector<char>>& board, const int row_num) {
  bool number_used[10] = {};
  for (const char& ch : board[row_num]) {
    if (!std::isdigit(ch)) continue;
    if (number_used[ch - '0'])
      return false;
    else
      number_used[ch - '0'] = true;
  }
  return true;
}

bool check_column(const vector<vector<char>>& board, const int column_num) {
  bool number_used[10] = {};
  for (const auto& row : board) {
    if (!std::isdigit(row[column_num])) continue;
    if (number_used[row[column_num] - '0'])
      return false;
    else
      number_used[row[column_num] - '0'] = true;
  }
  return true;
}

using block_left_top = std::pair<int, int>;

bool check_block(const vector<vector<char>>& board, const block_left_top& pos) {
  bool number_used[10] = {};
  for (int i = pos.first; i < pos.first + 3; i++) {
    for (int j = pos.second; j < pos.second + 3; j++) {
      if (!std::isdigit(board[i][j])) continue;
      if (number_used[board[i][j] - '0'])
        return false;
      else
        number_used[board[i][j] - '0'] = true;
    }
  }
  return true;
}

class Solution {
 public:
  bool isValidSudoku(const vector<vector<char>>& board) {
    print_board(board);
    bool ret = true;
    for (int i = 0; i < board.size(); i++) {
      ret &= check_column(board, i);
      ret &= check_row(board, i);
      if (!ret) return ret;
    }

    for (int i = 0; i < board.size(); i += 3)
      for (int j = 0; j < board[i].size(); j += 3)
        ret &= check_block(board, make_pair(i, j));
    return ret;
  }
};