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