Create crossword_puzzle_solver.py

backtracking/crossword_puzzle_solver.py

@@ -0,0 +1,127 @@
+"""
+    Solve a crossword puzzle by placing words from the provided list into the puzzle.
+
+    Args:
+        puzzle (List[List[str]]): The crossword puzzle grid.
+        words (List[str]): List of words to place in the puzzle.
+
+    Returns:
+        Optional[List[List[str]]]: The solved crossword puzzle, or None if no solution is found.
+"""
+from typing import List, Optional
+
+def solve_crossword(puzzle: List[List[str]], words: List[str]) -> Optional[List[List[str]]]:
+
+    rows, cols = len(puzzle), len(puzzle[0])
+
+    def is_valid_placement(word: str, row: int, col: int, direction: str) -> bool:
+        """
+        Check if placing a word in a specific direction at a given position is valid.
+
+        Args:
+            word (str): The word to be placed.
+            row (int): The starting row position.
+            col (int): The starting column position.
+            direction (str): Either "across" or "down".
+
+        Returns:
+            bool: True if the placement is valid, otherwise False.
+        """
+        if direction == "across":
+            return col + len(word) <= cols and all(puzzle[row][col + i] in ("", word[i]) for i in range(len(word)))
+        else:  # direction == "down"
+            return row + len(word) <= rows and all(puzzle[row + i][col] in ("", word[i]) for i in range(len(word)))
+
+    def place_word(word: str, row: int, col: int, direction: str) -> None:
+        """
+        Place a word in the crossword puzzle at a specific position and direction.
+
+        Args:
+            word (str): The word to be placed.
+            row (int): The starting row position.
+            col (int): The starting column position.
+            direction (str): Either "across" or "down".
+
+        Returns:
+            None
+        """
+        if direction == "across":
+            for i in range(len(word)):
+                puzzle[row][col + i] = word[i]
+        else:  # direction == "down"
+            for i in range(len(word)):
+                puzzle[row + i][col] = word[i]
+
+    def remove_word(word: str, row: int, col: int, direction: str) -> None:
+        """
+        Remove a word from the crossword puzzle at a specific position and direction.
+
+        Args:
+            word (str): The word to be removed.
+            row (int): The starting row position.
+            col (int): The starting column position.
+            direction (str): Either "across" or "down".
+
+        Returns:
+            None
+        """
+        if direction == "across":
+            for i in range(len(word)):
+                puzzle[row][col + i] = ""
+        else:  # direction == "down"
+            for i in range(len(word)):
+                puzzle[row + i][col] = ""
+
+    def backtrack(puzzle: List[List[str]], words: List[str]) -> bool:
+        """
+        Recursively backtrack to solve the crossword puzzle.
+
+        Args:
+            puzzle (List[List[str]]): The crossword puzzle grid.
+            words (List[str]): List of words to place in the puzzle.
+
+        Returns:
+            bool: True if a solution is found, otherwise False.
+        """
+        for row in range(rows):
+            for col in range(cols):
+                if puzzle[row][col] == "":
+                    for word in words[:]:
+                        for direction in ["across", "down"]:
+                            if is_valid_placement(word, row, col, direction):
+                                place_word(word, row, col, direction)
+                                words.remove(word)
+                                if not words:
+                                    return True
+                                if backtrack(puzzle, words):
+                                    return True
+                                words.append(word)
+                                remove_word(word, row, col, direction)
+                    return False
+        return True
+
+    # Create a copy of the puzzle to preserve the original
+    copied_puzzle = [row[:] for row in puzzle]
+    if backtrack(copied_puzzle, words):
+        return copied_puzzle
+    else:
+        return None
+
+# Example usage:
+puzzle = [
+    ["#", "#", "c", "#", "#", "#", "#"],
+    ["#", "#", "r", "a", "c", "k", "#"],
+    ["#", "#", "o", "#", "#", "#", "#"],
+    ["#", "#", "r", "#", "b", "#", "#"],
+    ["#", "#", "a", "a", "t", "a", "x"],
+    ["#", "#", "t", "#", "i", "n", "#"],
+    ["#", "#", "e", "#", "n", "#", "#"],
+]
+words = ["car", "rack", "bat", "cat", "rat", "in", "tax", "eat"]
+solution = solve_crossword(puzzle, words)
+
+if solution:
+    for row in solution:
+        print(" ".join(row))
+else:
+    print("No solution found.")