leetcode_36_Valid Sudoku

Valid Sudoku

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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.

//方法：时间复杂度O(n^2)，空间复杂度O(1)
class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        bool used[9];
        for(int i = 0; i < 9; i++)  //分别表示从1~9行，和1~9列
        {
            fill(used, used+9, false);  //检查行
            for(int j = 0; j < 9; j++)
            {
                if(!check(board[i][j], used))
                    return false;
            }
            
            fill(used, used+9, false);  //检查列
            for(int j = 0; j < 9; j++) 
            {
                if(!check(board[j][i], used))
                    return false;
            }
        }
        
        for(int i = 0; i < 9; i += 3)  //检查九3*3的正方形
            for(int j = 0; j < 9; j += 3)
            {
                fill(used, used+9, false);
                for(int k = 0; k < 3; k++)
                    for(int l = 0; l < 3; l++)
                    {
                        if(!check(board[i+k][j+l], used))
                            return false;
                    }
            }
        
        return true;
    }
    
    bool check(char ch, bool used[9])
    {
        if(ch == '.')
            return true;
        else if(used[ch - '1'] == false)
        {
            used[ch - '1'] = true;
            return true;
        }
        else if(used[ch - '1'] == true)
            return false;
    }
};