36. Valid Sudoku

36. Valid Sudoku

题目

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

The Sudoku board could be partially filled, where empty cells are filled with the character '.'.

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

解析

• 只是检测每行，每列，每个小方格是否满足九宫格的定义；使用hash表节省空间
• 另外就是小方格的坐标转换[i / 3 * 3 + j / 3][i % 3 * 3 + j % 3]需要技巧

// 36. Valid Sudoku 数独/九宫格问题
class Solution_36 {
public:
	bool isValidSudoku(vector<vector<char>>& board) {

		int row = board.size();
		int col = board[0].size();

		unordered_map<char,int> row_mp; // <char, bool>
		unordered_map<char,int> col_mp;
		unordered_map<char, int>  diagonal; //对角线; sub-boxes

		for (int i = 0; i < row;i++)
		{
			for (int j = 0; j < col;j++)
			{
				if (board[i][j]!='.' && row_mp.find(board[i][j])!=row_mp.end())
				{
					return false; //已经存在
				}
				else
				{
					row_mp[board[i][j]]++;
				}
				if (board[j][i] != '.'&& col_mp.find(board[j][i]) != col_mp.end())
				{
					return false;
				}
				else
				{
					col_mp[board[j][i]]++;
				}
				if (board[i / 3 * 3 + j / 3][i % 3 * 3 + j % 3] != '.'&& diagonal.find(board[i / 3 * 3 + j / 3][i % 3 * 3 + j % 3]) != diagonal.end()) // //第i个九宫格第j个格子
				{
					return false;
				}
				else
				{
					diagonal[board[i / 3 * 3 + j / 3][i % 3 * 3 + j % 3]]++;
				}
			}
			col_mp.clear();
			row_mp.clear();
			diagonal.clear();
		}
		return true;
	}
};

题目来源

• 36. Valid Sudoku