leetcode -- 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.

判断数独是否合法：

1. 同一行中1-9出现次数不重复

2. 同一列中1-9出现次数不重复

3. 9宫格中1-9出现次数不重复

这里将1,2的判断在一个循环体中进行，分开进行跑大数据集时会TLE

public boolean isValidSudoku(char[][] board) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(board.length == 0)
            return false;
        
        for(int i = 0; i < 9; i++){
            Set<Character> row = new HashSet<Character>();
            Set<Character> col = new HashSet<Character>();
            for(int j = 0; j < 9; j++){
                if(board[i][j] != '.'){
                    if(row.contains(board[i][j]))
                        return false;
                    else {
                        row.add(board[i][j]);
                    }
                }
                
                if(board[j][i] != '.'){
                    if(col.contains(board[j][i]))
                        return false;
                    else
                        col.add(board[j][i]);
                }
                
            }
        }
        
        for(int i = 0; i < 9; i+=3){
            for(int j = 0; j < 9; j+=3){
                Set<Character> container = new HashSet<Character>();
                for(int m = 0; m < 3; m++){
                    for(int n = 0; n < 3; n++){
                        if(board[m + i][n + j] == '.'){
                            continue;
                        }
                        if(container.contains(board[m + i][n + j]))
                            return false;
                        else {
                            container.add(board[m + i][n + j]);
                        }
                    }
                        
                }
                container.clear();
            }
        }
        return true;
        
    }