| 1 | 1 | def solve(puzzle: str) -> dict[str, int] | None: |
| 2 | | pass |
| 2 | """ |
| 3 | Solve an alphametics puzzle. |
| 4 | |
| 5 | Args: |
| 6 | puzzle: A string representing the alphametics puzzle (e.g., "SEND + MORE == MONEY") |
| 7 | |
| 8 | Returns: |
| 9 | A dictionary mapping letters to digits that solves the puzzle, or None if no solution exists. |
| 10 | |
| 11 | Example: |
| 12 | >>> solve("SEND + MORE == MONEY") |
| 13 | {'S': 9, 'E': 5, 'N': 6, 'D': 7, 'M': 1, 'O': 0, 'R': 8, 'Y': 2} |
| 14 | """ |
| 15 | # Parse the puzzle |
| 16 | if "==" not in puzzle: |
| 17 | return None |
| 18 | |
| 19 | left_side, right_side = puzzle.split("==") |
| 20 | left_side = left_side.strip() |
| 21 | right_side = right_side.strip() |
| 22 | |
| 23 | # Split the left side by '+' to get addends |
| 24 | addends = [term.strip() for term in left_side.split("+")] |
| 25 | |
| 26 | # Edge Case: Empty puzzle or invalid format |
| 27 | if not addends or not right_side: |
| 28 | return None |
| 29 | |
| 30 | # Get all unique letters |
| 31 | letters = set() |
| 32 | for term in addends + [right_side]: |
| 33 | letters.update(term) |
| 34 | |
| 35 | # Edge Case: No letters in puzzle |
| 36 | if not letters: |
| 37 | return None |
| 38 | |
| 39 | # Get first letters (can't be zero) |
| 40 | first_letters = {term[0] for term in addends + [right_side]} |
| 41 | |
| 42 | # Edge Case: More than 10 unique letters (impossible to solve) |
| 43 | if len(letters) > 10: |
| 44 | return None |
| 45 | |
| 46 | # Convert letters to list for indexing |
| 47 | letters_list = list(letters) |
| 48 | |
| 49 | # Try all permutations of digits for letters |
| 50 | from itertools import permutations |
| 51 | |
| 52 | # Edge Case: Handle single digit solutions |
| 53 | for perm in permutations(range(10), len(letters)): |
| 54 | mapping = dict(zip(letters_list, perm)) |
| 55 | |
| 56 | # Check if any first letter is assigned zero |
| 57 | if any(mapping[letter] == 0 for letter in first_letters): |
| 58 | continue |
| 59 | |
| 60 | # Convert words to numbers |
| 61 | try: |
| 62 | addend_values = [] |
| 63 | for addend in addends: |
| 64 | value = 0 |
| 65 | for char in addend: |
| 66 | value = value * 10 + mapping[char] |
| 67 | addend_values.append(value) |
| 68 | |
| 69 | right_value = 0 |
| 70 | for char in right_side: |
| 71 | right_value = right_value * 10 + mapping[char] |
| 72 | |
| 73 | # Check if the equation is satisfied |
| 74 | if sum(addend_values) == right_value: |
| 75 | return mapping |
| 76 | except KeyError: |
| 77 | # Edge Case: Mapping is incomplete (shouldn't happen with permutations but just in case) |
| 78 | continue |
| 79 | |
| 80 | # Edge Case: No solution found |
| 81 | return None |
| 82 | # Handled Edge Cases: Empty puzzle or invalid format, No letters in puzzle, More than 10 unique letters, Mapping is incomplete, No solution found, Handle single digit solutions |