36. Valid Sudoku 验证数独

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

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

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

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.

Difficulty: Medium

验证一个矩阵是否是数独矩阵,就是判断每行是否有重复的数字,每列是否有重复的数字,每个3x3的小矩阵是否有重复的数字.这个9x9里面有9个3x3的小矩阵,不计算重叠情况.这里用3个标志矩阵来记录对应位置是否出现过.

class Solution {
public:
    bool isValidSudoku(vector<vector<char>>& board) {
        if (board.empty()||board[0].empty()) return false;
        int m = board.size(),n = board[0].size();
        vector<vector<bool>> rowFlag(m,vector<bool>(n,false));
        vector<vector<bool>> colFlag(m,vector<bool>(n,false));
        vector<vector<bool>> cellFlag(m,vector<bool>(n,false));
        for (int i=0;i<m;++i){
            for (int j=0; j<n; ++j) {
                if (board[i][j]>='1'&&board[i][j]<='9'){
                    int c = board[i][j]-'1';
                    if (rowFlag[i][c] || colFlag[c][j] || cellFlag[3*(i/3) + j/3][c])
                    {
                        return false;
                    }
                    rowFlag[i][c] = true;
                    colFlag[c][j] = true;
                    cellFlag[3*(i/3) + j/3][c] = true;
                }
            }
        }
        return  true;
    }
};
 
comments powered by Disqus