Leetcode: 36. Valid Sudoku

Description

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 '.'.

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

思路

• 判断数独是否有效
• 即每一行不能出现重复，每一列不能出现重复，从上到下的每3 X 3 的小格子不能出现重复
• 用多个bitset<9>做映射，该位置0表未出现该数字，该位置1表出现
• 然后将9行，9列，9个小矩阵映射到27个bitset<9>上面

代码

• O(n^2)

class Solution {
public:
   bool isValidSudoku(vector<vector<char>>& board) {
		int m = board.size();
		int n = board[0].size();

		vector<bitset<9>> flag(27, 0);
		int num = 0;
		for (int i = 0; i < m; ++i){
			for (int j = 0; j < n; ++j){
				if (board[i][j] == '.') continue;
				else{
					num = board[i][j] - '1';
					if (flag[i].test(num) || flag[9 + j].test(num) || flag[18 + (i / 3) * 3 + j / 3].test(num)) 
						return false;
					else {
						flag[i].set(num);
						flag[9 + j].set(num);
						flag[18 + (i / 3) * 3 + j / 3].set(num);
					}
				}
			}
		}

		return true;
	}
};