[LeetCode] Valid Sudoku

Valid Sudoku

Determine if a Sudoku is valid, according to: Sudoku Puzzles - The Rules.

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

A partially filled sudoku which is valid.

Note:
A valid Sudoku board (partially filled) is not necessarily solvable. Only the filled cells need to be validated.

public class Solution {    public boolean isValidSudoku(char[][] board) {        Map<Integer, Boolean> map = new HashMap<Integer, Boolean>();// Validate each rowfor (int i = 0; i < board.length; i++) {for (int j = 0; j < board[0].length; j++) {if (board[i][j] != '.') {int key = board[i][j] - '0';if (map.get(key) == null) {map.put(key, true);} else {return false;}}}map.clear();}// Validate each columnfor (int j = 0; j < board[0].length; j++) {for (int i = 0; i < board.length; i++) {if (board[i][j] != '.') {int key = board[i][j] - '0';if (map.get(key) == null) {map.put(key, true);} else {return false;}}}map.clear();}// Validate each squarefor (int m = 0; m < 3; m++) {for (int n = 0; n < 3; n++) {for (int i = 0; i < 3; i++) {for (int j = 0; j < 3; j++) {if (board[3*m+i][3*n+j] != '.') {int key = board[3*m+i][3*n+j] - '0';if (map.get(key) == null) {map.put(key, true);} else {return false;}}}}map.clear();}}return true;}}