LeetCode 36. Valid Sudoku

题目描述:

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.

要求判断一个数独题目是否合法, 但并不要求一定有解. 一个数独题目合法有以下三个条件:

1. 每一行都没有重复元素
2. 每一列都没有重复元素
3. 九个3x3方格中都没有重复元素

因此验证这三个条件即可.

class Solution {
public:
    void setNumFlag(vector<int>& v){
        for(int i = 0; i < v.size(); i++) v[i] = 0;
    }
    bool isValidSudoku(vector<vector<char>>& board) {
        vector<int> numFlag(9);
        for(int i = 0; i < 9; i++){
            setNumFlag(numFlag);
            for(int j = 0; j < 9; j++){
                char t = board[i][j];
                if(t >= '1' && t <= '9'){
                    if(numFlag[t - '1'] == 1)
                        return false;
                    else
                        numFlag[t - '1'] = 1;
                }
            }
        }

        for(int i = 0; i < 9; i++){
            setNumFlag(numFlag);
            for(int j = 0; j < 9; j++){
                char t = board[j][i];
                if(t >= '1' && t <= '9'){
                    if(numFlag[t - '1'] == 1)
                        return false;
                    else
                        numFlag[t - '1'] = 1;
                }
            }
        }

        for(int i = 0; i < 3; i++){
            for(int j = 0; j < 3; j++){
                int x = i * 3, y = j * 3;
                setNumFlag(numFlag);
                for(int ii = 0; ii < 3; ii++){
                    for(int jj = 0; jj < 3; jj++){
                        char t = board[x + ii][y + jj];
                        if(t >= '1' && t <= '9'){
                            if(numFlag[t - '1'] == 1)
                                return false;
                            else
                                numFlag[t - '1'] = 1;
                        }
                    }
                }
            }
        }

        return true;
    }
};