[36] leetcode valid Sudoku (hash table)

Topic links: https://leetcode-cn.com/problems/valid-sudoku/

Title Description

Determining a number of unique 9x9 is valid. Only according to the following rules, to verify whether the numbers already filled can be effective.

1. The numbers 1-9 appear only once in each row.
2. The numbers 1-9 appear only once in each column.
3. Figures 1-9 only appear once in each 3x3 intrauterine separated by a thick solid line.

The figure is the number of valid only a partially filled.

Sudoku part of this space has been filled in the numbers, empty cells with '.' Representation.

Example 1:

输入:
[
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
输出: true

Example 2:

输入:
[
  ["8","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
输出: false
解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。
     但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。

Description:

• Only a valid number (portion has been filled) is not necessarily solvable.
• According to the above rules only need to verify whether the figures have been filled can be effective.
• Given the number of unique sequence comprises only numeric characters 1-9 and '.'.
• Sudoku will always be given in the form of 9x9.

Thinking

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        unordered_set<char> s;
        // 检查每一行
        for (int i = 0; i < board.size(); ++i) {
            s.clear();
            for (int j = 0; j < board[0].size(); ++j) {
                if(board[i][j] != '.'){
                    if(s.count(board[i][j]) == 0)
                        s.insert(board[i][j]);
                    else
                        return false;
                }
            }
        }
        // 检查每一列
        for (int j = 0; j < board[0].size(); ++j) {
            s.clear();
            for (int i = 0; i < board.size(); ++i) {
                if(board[i][j] != '.'){
                    if(s.count(board[i][j]) == 0)
                        s.insert(board[i][j]);
                    else
                        return false;
                }
            }
        }

        // 检查每个九宫格
        for (int k = 0; k < 9; ++k) {
            int x = k /3 * 3, y = (k %3) * 3;
            s.clear();
            for (int i = x; i < x+3; ++i) {
                for (int j = y; j < y+3; ++j) {
                    if(board[i][j] != '.'){
                        if(s.count(board[i][j]) == 0)
                            s.insert(board[i][j]);
                        else
                            return false;
                    }
                }
            }
        }
        return true;
    }
};