Added validate sudoku board function

graphs/deep_clone_graph.py

@@ -0,0 +1,77 @@
+"""
+LeetCode 133. Clone Graph
+https://leetcode.com/problems/clone-graph/
+
+Given a reference of a node in a connected undirected graph.
+
+Return a deep copy (clone) of the graph.
+
+Each node in the graph contains a value (int) and a list (List[Node]) of its
+neighbors.
+"""
+from dataclasses import dataclass
+
+
+@dataclass
+class Node:
+    value: int = 0
+    neighbors: list["Node"] | None = None
+
+    def __post_init__(self) -> None:
+        """
+        >>> Node(3).neighbors
+        []
+        """
+        self.neighbors = self.neighbors or []
+
+    def __hash__(self) -> int:
+        """
+        >>> hash(Node(3)) != 0
+        True
+        """
+        return id(self)
+
+
+def clone_graph(node: Node | None) -> Node | None:
+    """
+    This function returns a clone of a connected undirected graph.
+    >>> clone_graph(Node(1))
+    Node(value=1, neighbors=[])
+    >>> clone_graph(Node(1, [Node(2)]))
+    Node(value=1, neighbors=[Node(value=2, neighbors=[])])
+    >>> clone_graph(None) is None
+    True
+    """
+    if not node:
+        return None
+
+    originals_to_clones = {}  # map nodes to clones
+
+    stack = [node]
+
+    while stack:
+        original = stack.pop()
+
+        if original in originals_to_clones:
+            continue
+
+        originals_to_clones[original] = Node(original.value)
+
+        stack.extend(original.neighbors or [])
+
+    for original, clone in originals_to_clones.items():
+        for neighbor in original.neighbors or []:
+            cloned_neighbor = originals_to_clones[neighbor]
+
+            if not clone.neighbors:
+                clone.neighbors = []
+
+            clone.neighbors.append(cloned_neighbor)
+
+    return originals_to_clones[node]
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()

matrix/validate_sudoku_board.py

@@ -0,0 +1,99 @@
+"""
+LeetCode 36. Valid Sudoku
+https://leetcode.com/problems/valid-sudoku/
+https://en.wikipedia.org/wiki/Sudoku
+
+Determine if a 9 x 9 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 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.
+"""
+
+from collections import defaultdict
+
+NUM_ROWS = 9
+NUM_COLS = 9
+EMPTY_CELL = "."
+IS_VALID = True
+
+
+def is_valid_sudoku_board(sudoku_board: list[list[str]]) -> bool:
+    """
+    This function validates (but does not solve) a sudoku board.
+    The board may be valid but unsolvable.
+
+    >>> is_valid_sudoku_board([
+    ...  ["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"]
+    ... ])
+    True
+    >>> is_valid_sudoku_board([
+    ...  ["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"]
+    ... ])
+    False
+    >>> is_valid_sudoku_board([["1", "2", "3", "4", "5", "6", "7", "8", "9"]])
+    Traceback (most recent call last):
+        ...
+    Exception: Number of rows must be 9.
+    >>> is_valid_sudoku_board([["1"], ["2"], ["3"], ["4"], ["5"], ["6"], ["7"], ["8"], ["9"]])
+    Traceback (most recent call last):
+        ...
+    Exception: Number of columns must be 9.
+    """
+    if len(sudoku_board) != NUM_ROWS:
+        raise Exception("Number of rows must be 9.")
+
+    for row in sudoku_board:
+        if len(row) != NUM_COLS:
+            raise Exception("Number of columns must be 9.")
+
+    row_values = defaultdict(set)  # maps each row to a set
+    col_values = defaultdict(set)  # maps each col to a set
+    box_values = defaultdict(set)  # maps each 3x3 box to a set
+
+    for row in range(NUM_ROWS):
+        for col in range(NUM_COLS):
+            value = sudoku_board[row][col]
+
+            if value == EMPTY_CELL:
+                continue
+
+            box = (row // 3, col // 3)
+
+            if (
+                value in row_values[row]
+                or value in col_values[col]
+                or value in box_values[box]
+            ):
+                return not IS_VALID
+
+            row_values[row].add(value)
+            col_values[col].add(value)
+            box_values[box].add(value)
+
+    return IS_VALID