[leetcode] 36. Valid Sudoku

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.

这道题是判断部分填充好的数独是否正确，不考虑没有填充的部分，题目难度为easy。

不熟悉数独游戏的同学请问度娘，这里不再详细介绍规则。题目没有要求找出结果，第37题会给出求解的过程。这里只需要判断每行、每列、每个小的九宫格中是否有重复的数字即可，很自然会选用Hash Table来存储已经出现过的数字。具体代码：

class Solution {public:    bool isValidSudoku(vector<vector<char>>& board) {        vector<unordered_set<char>> rows(9), cols(9), grid(9);        for(int i=0; i<9; ++i) {            for(int j=0; j<9; ++j) {                if(board[i][j] == '.') continue;                if(rows[i].find(board[i][j]) != rows[i].end()) return false;                else rows[i].insert(board[i][j]);                if(cols[j].find(board[i][j]) != cols[j].end()) return false;                else cols[j].insert(board[i][j]);                int n = i - i%3 + j/3;                if(grid[n].find(board[i][j]) != grid[n].end()) return false;                else grid[n].insert(board[i][j]);            }        }        return true;    }};