| 1 | from itertools import permutations |
| 2 | import re |
| 3 | |
| 1 | 4 | def solve(puzzle: str) -> dict[str, int] | None: |
| 2 | | pass |
| 5 | """ |
| 6 | Solve an alphametics puzzle. |
| 7 | |
| 8 | Args: |
| 9 | puzzle (str): The alphametics puzzle string in the format "A + B == C" |
| 10 | |
| 11 | Returns: |
| 12 | dict[str, int] | None: A dictionary mapping letters to digits that solves the puzzle, |
| 13 | or None if no solution exists. |
| 14 | |
| 15 | Example: |
| 16 | >>> solve("SEND + MORE == MONEY") |
| 17 | {'S': 9, 'E': 5, 'N': 6, 'D': 7, 'M': 1, 'O': 0, 'R': 8, 'Y': 2} |
| 18 | """ |
| 19 | # Parse the puzzle into components |
| 20 | # Edge Case: Invalid puzzle format |
| 21 | if "==" not in puzzle: |
| 22 | return None |
| 23 | |
| 24 | left_side, right_side = puzzle.split("==") |
| 25 | left_side = left_side.strip() |
| 26 | right_side = right_side.strip() |
| 27 | |
| 28 | # Extract all words (sequences of uppercase letters) |
| 29 | words = re.findall(r'[A-Z]+', puzzle) |
| 30 | if not words: |
| 31 | return None |
| 32 | |
| 33 | # Edge Case: No words found in puzzle |
| 34 | if not words: |
| 35 | return None |
| 36 | |
| 37 | # Get all unique letters |
| 38 | unique_letters = set(''.join(words)) |
| 39 | |
| 40 | # Edge Case: More than 10 unique letters (impossible to solve) |
| 41 | if len(unique_letters) > 10: |
| 42 | return None |
| 43 | |
| 44 | # Get the first letter of each word (can't be zero) |
| 45 | first_letters = {word[0] for word in words} |
| 46 | |
| 47 | # Edge Case: Empty puzzle |
| 48 | if not unique_letters: |
| 49 | return None |
| 50 | |
| 51 | # Try all permutations of digits for the unique letters |
| 52 | for perm in permutations(range(10), len(unique_letters)): |
| 53 | mapping = dict(zip(unique_letters, perm)) |
| 54 | |
| 55 | # Edge Case: Leading zero in any word |
| 56 | if any(mapping[letter] == 0 for letter in first_letters): |
| 57 | continue |
| 58 | |
| 59 | # Convert words to numbers using the current mapping |
| 60 | numbers = [] |
| 61 | for word in words: |
| 62 | num = 0 |
| 63 | for letter in word: |
| 64 | num = num * 10 + mapping[letter] |
| 65 | numbers.append(num) |
| 66 | |
| 67 | # Check if the equation is satisfied |
| 68 | # The last number is the result, the rest are addends |
| 69 | if sum(numbers[:-1]) == numbers[-1]: |
| 70 | return mapping |
| 71 | |
| 72 | # Edge Case: No solution found |
| 73 | return None |
| 74 | |
| 75 | # Handled Edge Cases: Invalid puzzle format, No words found in puzzle, More than 10 unique letters, Empty puzzle, Leading zero in any word, No solution found |