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leetcode笔记：36. valid sudoku

admin 11月 14, 2020 0

# Title Difficulty Topic
36 Valid Sudoku Medium Hash Table

Description

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.

Sudoku
A partially filled sudoku which is valid.

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

Example 1:

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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:

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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.

Array

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class  {
    public boolean isValidSudoku(char[][] board) {
        boolean[] exists = new boolean[9];
        for(int i=0; i<9; i++) {
            Arrays.fill(exists, false);
            for(int j=0; j<9; j++) {
                if(board[i][j] == '.') continue;
                if(exists[board[i][j]-'1']) return false;
                else exists[board[i][j]-'1'] = true;
            }
        }
        for(int j=0; j<9; j++) {
            Arrays.fill(exists, false);
            for(int i=0; i<9; i++) {
                if(board[i][j] == '.') continue;
                if(exists[board[i][j]-'1']) return false;
                else exists[board[i][j]-'1'] = true;
            }
        }
        for(int m=0; m<3; m++) {
            for(int n=0; n<3; n++) {
                Arrays.fill(exists, false);
                for(int i=m*3; i<(m+1)*3; i++) {
                    for(int j=n*3; j<(n+1)*3; j++) {
                        if(board[i][j] == '.') continue;
                        if(exists[board[i][j]-'1']) return false;
                        else exists[board[i][j]-'1'] = true;
                    }
                }
            }
        }
        return true;
    }
}
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