<p>Determine if a&nbsp;<code>9 x 9</code> Sudoku board&nbsp;is valid.&nbsp;Only the filled cells need to be validated&nbsp;<strong>according to the following rules</strong>:</p>

<ol>
	<li>Each row&nbsp;must contain the&nbsp;digits&nbsp;<code>1-9</code> without repetition.</li>
	<li>Each column must contain the digits&nbsp;<code>1-9</code>&nbsp;without repetition.</li>
	<li>Each of the nine&nbsp;<code>3 x 3</code> sub-boxes of the grid must contain the digits&nbsp;<code>1-9</code>&nbsp;without repetition.</li>
</ol>

<p><strong>Note:</strong></p>

<ul>
	<li>A Sudoku board (partially filled) could be valid but is not necessarily solvable.</li>
	<li>Only the filled cells need to be validated according to the mentioned&nbsp;rules.</li>
</ul>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img src="https://upload.wikimedia.org/wikipedia/commons/thumb/f/ff/Sudoku-by-L2G-20050714.svg/250px-Sudoku-by-L2G-20050714.svg.png" style="height:250px; width:250px" />
<pre>
<strong>Input:</strong> board = 
[[&quot;5&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;]
,[&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;,&quot;9&quot;,&quot;5&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;]
,[&quot;.&quot;,&quot;9&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;]
,[&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;3&quot;]
,[&quot;4&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;]
,[&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;]
,[&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;8&quot;,&quot;.&quot;]
,[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;4&quot;,&quot;1&quot;,&quot;9&quot;,&quot;.&quot;,&quot;.&quot;,&quot;5&quot;]
,[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;9&quot;]]
<strong>Output:</strong> true
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> board = 
[[&quot;8&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;]
,[&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;,&quot;9&quot;,&quot;5&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;]
,[&quot;.&quot;,&quot;9&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;]
,[&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;3&quot;]
,[&quot;4&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;3&quot;,&quot;.&quot;,&quot;.&quot;,&quot;1&quot;]
,[&quot;7&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;6&quot;]
,[&quot;.&quot;,&quot;6&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;2&quot;,&quot;8&quot;,&quot;.&quot;]
,[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;4&quot;,&quot;1&quot;,&quot;9&quot;,&quot;.&quot;,&quot;.&quot;,&quot;5&quot;]
,[&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;.&quot;,&quot;8&quot;,&quot;.&quot;,&quot;.&quot;,&quot;7&quot;,&quot;9&quot;]]
<strong>Output:</strong> false
<strong>Explanation:</strong> Same as Example 1, except with the <strong>5</strong> in the top left corner being modified to <strong>8</strong>. Since there are two 8&#39;s in the top left 3x3 sub-box, it is invalid.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>board.length == 9</code></li>
	<li><code>board[i].length == 9</code></li>
	<li><code>board[i][j]</code> is a digit <code>1-9</code> or <code>&#39;.&#39;</code>.</li>
</ul>

class Solution:
    def isValidSudoku(self, board: List[List[str]]) -> bool:
        # hashmap/set for each scenario: rows, columns, sub-boxes

        rows = defaultdict(list)
        columns = defaultdict(list)
        subboxes = defaultdict(list)

        # go through and add to according ones
        for row in range(len(board)):
            for col in range(len(board[row])):
                number = board[row][col]

                if not number.isdigit():
                    continue

                subbox = (row // 3, col // 3)

                if number in rows[row] or number in columns[col] or number in subboxes[subbox]:
                    return False
                
                else:
                    rows[row].append(number)
                    columns[col].append(number)
                    subboxes[subbox].append(number)
        
        return True


                


        
        
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