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.

判斷每行 每列和每個3*3方塊中有沒有重復的

 1 public boolean isValidSudoku(char[][] board) {//set mytip
 2         Set<String> set = new HashSet<>();
 3         for (int i = 0; i < board.length; i++) {
 4             for (int j = 0; j < board.length; j++) {
 5                 if (‘.‘!=board[i][j]){
 6                     String s1 = board[i][j]+"-"+i;
 7                     String s2 = board[i][j]+"|"+j;
 8                     String s3 = board[i][j]+"#"+(i/3*3+j/3);
 9                     if(set.contains(s1)||set.contains(s2)||set.contains(s3)){
10                         return false;
11                     }
12                     else{
13                         set.add(s1);
14                         set.add(s2);
15                         set.add(s3);
16                     }
17                 }
18             }
19         }
20         return true;
21     }

進階題

數獨 LeetCode37 https://www.cnblogs.com/zhacai/p/10622800.html

LeetCode-36.Valid Sudoku