| 1 | import itertools |
| 2 | import re |
| 3 | |
| 1 | 4 | def solve(puzzle: str) -> dict[str, int] | None: |
| 2 | | pass |
| 5 | # Remove spaces and split by '==' to get left and right parts |
| 6 | parts = puzzle.replace(" ", "").split("==") |
| 7 | |
| 8 | # Edge Case: Invalid puzzle format with incorrect number of parts |
| 9 | if len(parts) != 2: |
| 10 | return None |
| 11 | |
| 12 | left_side, right_side = parts |
| 13 | |
| 14 | # Split the left side by '+' to get addends |
| 15 | addends = left_side.split("+") |
| 16 | |
| 17 | # Extract all unique letters from the puzzle |
| 18 | letters = set(re.findall(r'[A-Z]', puzzle)) |
| 19 | |
| 20 | # Edge Case: No letters in puzzle |
| 21 | if not letters: |
| 22 | return None |
| 23 | |
| 24 | # Extract first letters of each word (cannot be zero) |
| 25 | first_letters = {word[0] for word in addends + [right_side]} |
| 26 | |
| 27 | # Edge Case: More than 10 unique letters (impossible to assign unique digits) |
| 28 | if len(letters) > 10: |
| 29 | return None |
| 30 | |
| 31 | # Generate all possible digit permutations for the unique letters |
| 32 | for perm in itertools.permutations(range(10), len(letters)): |
| 33 | mapping = dict(zip(letters, perm)) |
| 34 | |
| 35 | # Edge Case: Leading zero in any word |
| 36 | if any(mapping[first_letter] == 0 for first_letter in first_letters): |
| 37 | continue |
| 38 | |
| 39 | # Convert words to numbers using the current mapping |
| 40 | try: |
| 41 | addend_values = [int(''.join(str(mapping[c]) for c in word)) for word in addends] |
| 42 | right_value = int(''.join(str(mapping[c]) for c in right_side)) |
| 43 | except KeyError: |
| 44 | # Edge Case: Mapping is incomplete (should not happen with correct permutation logic) |
| 45 | continue |
| 46 | |
| 47 | # Check if the sum of addends equals the right side value |
| 48 | if sum(addend_values) == right_value: |
| 49 | return mapping |
| 50 | |
| 51 | # Edge Case: No valid solution found |
| 52 | return None |
| 53 | # Handled Edge Cases: Invalid puzzle format, no letters in puzzle, more than 10 unique letters, leading zero in any word, incomplete mapping, no valid solution found |