#include "s0037_sudoku_solver.hpp"

// 返回结果为当前传递进去的数独是否存在解
bool S0037::recusiveSolveSudoku(vector<vector<char>> &board,
                                vector<unordered_map<char, bool>> &rows,
                                vector<unordered_map<char, bool>> &cols,
                                vector<unordered_map<char, bool>> &grids,
                                int row, int col) {
  int size = board.size();
  // 边界校验
  if (col == size) {
    // 进入下一行
    col = 0;
    row++;
    // 填充完成，返回 True
    if (row == size) {
      return true;
    }
  }
  // 如果不为空则跳过，填充下一个
  if (board[row][col] != '.') {
    return recusiveSolveSudoku(board, rows, cols, grids, row, col + 1);
  } else {  // 否则开始填充
    // 尝试填充 1 ~ 9
    for (char num{'1'}; num <= '9'; ++num) {
      int gridIndex = static_cast<int>(floor(row / 3)) +
                      3 * static_cast<int>(floor(col / 3));
      // 如果这个数字还没有出现过
      if (!(rows[row].count(num) == 1 || cols[col].count(num) == 1 ||
            grids[gridIndex].count(num) == 1)) {
        // 先把这个数字填进去
        rows[row][num] = true;
        cols[col][num] = true;
        grids[gridIndex][num] = true;
        board[row][col] = num;
        // 然后试试看填进去后下一个能不能解
        // 如果下一个能解的话，现在这个肯定能解
        if (recusiveSolveSudoku(board, rows, cols, grids, row, col + 1)) {
          return true;
        }
        // 如果不能解，那么说明这个数字填错了，把它重新设为空，然后尝试下一个数字
        board[row][col] = '.';
        rows[row].erase(num);
        cols[col].erase(num);
        grids[gridIndex].erase(num);
      }
    }
  }
  return false;
}

void S0037::solveSudoku(vector<vector<char>> &board) {
  // 每个行/列/单元格中某个数字是否出现过
  vector<unordered_map<char, bool>> rows;
  vector<unordered_map<char, bool>> cols;
  vector<unordered_map<char, bool>> grids;
  // 初始化
  int size = board.size();
  for (int i{0}; i < size; ++i) {
    rows.push_back(unordered_map<char, bool>{});
    cols.push_back(unordered_map<char, bool>{});
    grids.push_back(unordered_map<char, bool>{});
  }
  for (int row{0}; row < size; ++row) {
    for (int col{0}; col < size; ++col) {
      if (board[row][col] != '.') {
        rows[row][board[row][col]] = true;
        cols[col][board[row][col]] = true;
        int gridIndex = static_cast<int>(floor(row / 3)) +
                        3 * static_cast<int>(floor(col / 3));
        grids[gridIndex][board[row][col]] = true;
      }
    }
  }
  // 从 (0, 0) 开始递归求解
  recusiveSolveSudoku(board, rows, cols, grids, 0, 0);
}