Added validate sudoku board function

matrix/validate_sudoku_board.py

@@ -0,0 +1,101 @@
+"""
+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[int, set[str]] = defaultdict(set)
+    col_values: defaultdict[int, set[str]] = defaultdict(set)
+    box_values: defaultdict[tuple[int, int], set[str]] = defaultdict(set)
+
+    for r in range(NUM_ROWS):
+        for c in range(NUM_COLS):
+            value = sudoku_board[r][c]
+
+            if value == EMPTY_CELL:
+                continue
+
+            box = (r // 3, c // 3)
+
+            if (
+                value in row_values[r]
+                or value in col_values[c]
+                or value in box_values[box]
+            ):
+                return not IS_VALID
+
+            row_values[r].add(value)
+            col_values[c].add(value)
+            box_values[box].add(value)
+
+    return IS_VALID