| 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 | # Edge Case: Empty or None puzzle |
| 16 | if not puzzle: |
| 17 | return None |
| 18 | |
| 19 | # Parse the puzzle |
| 20 | parts = puzzle.replace("==", "=").replace(" ", "").split("=") |
| 21 | |
| 22 | # Edge Case: Invalid puzzle format (no equals sign or too many parts) |
| 23 | if len(parts) != 2: |
| 24 | return None |
| 25 | |
| 26 | right_side = parts[1] |
| 27 | left_parts = parts[0].replace("+", " ").split() |
| 28 | |
| 29 | # Edge Case: No terms on the left side |
| 30 | if not left_parts: |
| 31 | return None |
| 32 | |
| 33 | # Check if right side is a numeric constant |
| 34 | if right_side.isdigit(): |
| 35 | target_value = int(right_side) |
| 36 | # Extract letters only from left side |
| 37 | letters = set() |
| 38 | for part in left_parts: |
| 39 | letters.update(part) |
| 40 | right_side_letters = "" |
| 41 | else: |
| 42 | # Right side contains letters |
| 43 | target_value = None |
| 44 | # Extract all unique letters |
| 45 | letters = set() |
| 46 | for part in left_parts + [right_side]: |
| 47 | letters.update(part) |
| 48 | right_side_letters = right_side |
| 49 | |
| 50 | # Edge Case: No letters in puzzle |
| 51 | if not letters: |
| 52 | # Special case: if it's a pure numeric equation like "5 == 5" |
| 53 | if target_value is not None: |
| 54 | left_values = [] |
| 55 | for word in left_parts: |
| 56 | if word.isdigit(): |
| 57 | left_values.append(int(word)) |
| 58 | else: |
| 59 | # This shouldn't happen in a valid puzzle with no letters |
| 60 | return None |
| 61 | if sum(left_values) == target_value: |
| 62 | return {} |
| 63 | return None |
| 64 | |
| 65 | # Extract first letters (can't be zero) |
| 66 | first_letters = {word[0] for word in left_parts} |
| 67 | if right_side_letters: |
| 68 | first_letters.add(right_side_letters[0]) |
| 69 | |
| 70 | # Convert letters to a list for indexing |
| 71 | letters_list = list(letters) |
| 72 | |
| 73 | # Try all permutations of digits for the letters |
| 74 | from itertools import permutations |
| 75 | |
| 76 | # Edge Case: More letters than digits (0-9) |
| 77 | if len(letters_list) > 10: |
| 78 | return None |
| 79 | |
| 80 | # Try all digit assignments |
| 81 | for perm in permutations(range(10), len(letters_list)): |
| 82 | mapping = dict(zip(letters_list, perm)) |
| 83 | |
| 84 | # Edge Case: Leading zero in any number |
| 85 | if any(mapping[first] == 0 for first in first_letters): |
| 86 | continue |
| 87 | |
| 88 | # Calculate values of left side terms |
| 89 | left_values = [] |
| 90 | for word in left_parts: |
| 91 | if word.isdigit(): |
| 92 | left_values.append(int(word)) |
| 93 | else: |
| 94 | value = 0 |
| 95 | for char in word: |
| 96 | value = value * 10 + mapping[char] |
| 97 | left_values.append(value) |
| 98 | |
| 99 | # Calculate value of right side |
| 100 | if target_value is not None: |
| 101 | right_value = target_value |
| 102 | else: |
| 103 | right_value = 0 |
| 104 | for char in right_side_letters: |
| 105 | right_value = right_value * 10 + mapping[char] |
| 106 | |
| 107 | # Check if equation is satisfied |
| 108 | if sum(left_values) == right_value: |
| 109 | return mapping |
| 110 | |
| 111 | # Edge Case: No valid solution found |
| 112 | return None |
| 113 | |
| 114 | # Handled Edge Cases: Empty or None puzzle, Invalid puzzle format, No terms on left side, No letters in puzzle, More letters than digits, Leading zero in any number, No valid solution found |