判断数独

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Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

1. Each row must contain the digits 1-9 without repetition.
2. Each column must contain the digits 1-9 without repetition.
3. Each of the 9 3x3 sub-boxes of the grid must contain the digits 1-9 without repetition.

A partially filled sudoku which is valid.

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

Example 1:

Input:
[
  ["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"]
]
Output: true

Example 2:

Input:
[
  ["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"]
]
Output: false
Explanation: Same as Example 1, except with the 5 in the top left corner being 
    modified to 8. Since there are two 8's in the top left 3x3 sub-box, it is invalid.

Note:

• A Sudoku board (partially filled) could be valid but is not necessarily solvable.
• Only the filled cells need to be validated according to the mentioned rules.
• The given board contain only digits 1-9 and the character '.'.
• The given board size is always 9x9.

哈希表实现，分别判断行，列，与9个3*3小格

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        unordered_map<char,int> hash;
        //row
        for(int i=0;i<9;i++)
        {
            for(int j=0;j<9;j++)
            {
                if(board[i][j]=='.')
                    continue;
                if(hash.find(board[i][j])==hash.end())
                {
                    hash[board[i][j]]++;
                    continue;
                }    
                return false;
            }
            hash.clear();
        }
        hash.clear();
        //col
        for(int i=0;i<9;i++)
        {
            for(int j=0;j<9;j++)
            {
                if(board[j][i]=='.')
                    continue;
                if(hash.find(board[j][i])==hash.end())
                {
                    hash[board[j][i]]++;
                    continue;
                }    
                return false;
            }
            hash.clear();
        }
        hash.clear();
        //3*3cube
        for(int i=0;i<9;i++)
        {
            //注意逐个取3*3小格的取法，行：3*(i/3)--3+3*(i/3),列：3*(i%3)--3+3*(i%3)
            for(int j=3*(i/3);j<3+3*(i/3);j++)
            {
                for(int k=3*(i%3);k<3+3*(i%3);k++)
                {
                    if(board[j][k]=='.')
                        continue;
                    if(hash.find(board[j][k])==hash.end())
                    {
                        hash[board[j][k]]++;
                        continue;
                    } 
                    return false;
                }
            }
            hash.clear();
        }
        return true;
    }
};