36. Valid Sudoku

Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:

Each row must contain the digits 1-9 without repetition.Each column must contain the digits 1-9 without repetition.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.

//别人的代码...

class Solution { public boolean isValidSudoku(char[][] board) { Set<String> seen = new HashSet<>(); for(int i = 0;i<board.length;i++){ for(int j =0;j<board[0].length;j++){ if(board[i][j]!='.'){ if( !seen.add(board[i][j]+" in row " + i) || !seen.add(board[i][j]+" in column " + j) || !seen.add(board[i][j]+" in block " + i/3 + ',' + j/3) ){ return false; } } } } return true; } }