36. 有效的数独

Posted 2021-03-02 zzytxl

36. 有效的数独

判断一个 9x9 的数独是否有效。只需要根据以下规则，验证已经填入的数字是否有效即可。

1. 数字 1-9 在每一行只能出现一次。
2. 数字 1-9 在每一列只能出现一次。
3. 数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。

上图是一个部分填充的有效的数独。

数独部分空格内已填入了数字，空白格用 ‘.‘ 表示。

示例 1:

输入:
[
  ["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"]
]
输出: true

示例 2:

输入:
[
  ["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"]
]
输出: false
解释: 除了第一行的第一个数字从 5 改为 8 以外，空格内其他数字均与 示例1 相同。
     但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。

说明:

• 一个有效的数独（部分已被填充）不一定是可解的。
• 只需要根据以上规则，验证已经填入的数字是否有效即可。
• 给定数独序列只包含数字 1-9 和字符 ‘.‘ 。
• 给定数独永远是 9x9 形式的。

class Solution {
    public boolean isValidSudoku(char[][] board) {
        if(board == null || board.length == 0 || board[0].length == 0) return false;
        //3个HashSet，
        HashMap<Character,Integer>[] rMaps = new HashMap[9];
        HashMap<Character,Integer>[] cMaps = new HashMap[9];
        HashMap<Character,Integer>[] boxMaps = new HashMap[9];
        for(int i = 0;i < 9;i++){
            rMaps[i] = new HashMap<>();
            cMaps[i] = new HashMap<>();
            boxMaps[i] = new HashMap<>();            
        }
        // int m = board.length,n = board[0].length;
        for(int i = 0;i < 9;i++){
            for(int j = 0;j < 9;j++){
               char c = board[i][j];
                if(c != ‘.‘){
                    int boxIndex = (i / 3) * 3 + j / 3;
                    rMaps[i].put(c,rMaps[i].getOrDefault(c,0) + 1);
                    cMaps[j].put(c,cMaps[j].getOrDefault(c,0) + 1);
                    boxMaps[boxIndex].put(c,boxMaps[boxIndex].getOrDefault(c,0) + 1);

                    if(rMaps[i].get(c) > 1 || cMaps[j].get(c) > 1 || boxMaps[boxIndex].get(c) > 1){
                        return false;
                    }
                }
            }
        }            
        return true;
         
    }
}