36. Valid Sudoku

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.

解析

给定一个一个二维数组代表数独的数据，判断是否满足数独的条件。有三个条件一个是：每列不能有重复的字符，每行不能有重复的数字，每个3*3的小块不能有重复的数字。

参考答案（自己写的）

class Solution {
    public boolean isValidSudoku(char[][] board) {
        List<Set<Character>> colList = new ArrayList<>();
        List<Set<Character>> subBoxList = new ArrayList<>();
        for (int i = 0; i < 9; i++) {
            colList.add(new HashSet<>());
            subBoxList.add(new HashSet<>());
        }
        for (int i = 0; i < board.length; i++) {
            Set<Character> row = new HashSet<>();
            for (int j = 0; j < board.length; j++) {
                if (board[i][j] != '.') {
                    if (row.contains(board[i][j])) {
                        return false;
                    } else {
                        row.add(board[i][j]);
                    }
                    if (colList.get(j).contains(board[i][j])) {
                        return false;
                    } else {
                        colList.get(j).add(board[i][j]);
                    }
                    int index = (i / 3) * 3 + j / 3;
                    if (subBoxList.get(index).contains(board[i][j])) {
                        return false;
                    } else {
                        subBoxList.get(index).add(board[i][j]);
                    }
                }
            }
        }
        return true;
    }
}

用2个List<Set