36. Valid Sudoku

问题
Determine if a 9 x 9 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 nine 3 x 3 sub-boxes of the grid must contain the digits 1-9 without repetition.

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.

遍历并创建三组不同的哈希表，每个表内包含一组哈希集合。
如果访问的元素已在哈希集合内，则返回false

class Solution {
    public boolean isValidSudoku(char[][] board) {
        HashMap<Integer,HashSet<Character>> rowMap = new HashMap<Integer,HashSet<Character>>();
        HashMap<Integer,HashSet<Character>> colMap = new HashMap<Integer,HashSet<Character>>();
        HashMap<Integer,HashSet<Character>> blockMap = new HashMap<Integer,HashSet<Character>>();

        for (int i = 0; i < board[0].length; i++ ){
            for (int j = 0; j < board.length; j++ ){
                char curChar = board[i][j];
                if (curChar == '.'){
                    continue;
                }
                if (!rowMap.containsKey(i)){
                    rowMap.put(i, new HashSet<Character>());
                }
                if (!colMap.containsKey(j)){
                    colMap.put(j, new HashSet<Character>());
                }
                if (!blockMap.containsKey(j/3*3+i/3)){
                    blockMap.put(j/3*3+i/3, new HashSet<Character>());
                }
                HashSet<Character> curRow = rowMap.get(i);
                HashSet<Character> curCol = colMap.get(j);
                HashSet<Character> curBlock = blockMap.get(j/3*3+i/3);
                
                if ( !curRow.contains(curChar) && !curCol.contains(curChar) && !curBlock.contains(curChar) ){
                    curRow.add(curChar);
                    curCol.add(curChar);
                    curBlock.add(curChar);
                }
                else{
                    return false;
                }   
            }
        }
        return true;
    }
}