| 1 | 1 | def answer(question: str) -> int: |
| 2 | | pass |
| 2 | """ |
| 3 | Parse and evaluate a simple math word problem. |
| 4 | |
| 5 | Args: |
| 6 | question: A string representing a math word problem |
| 7 | |
| 8 | Returns: |
| 9 | int: The result of evaluating the math expression |
| 10 | |
| 11 | Raises: |
| 12 | ValueError: If the question is malformed, contains unknown operations, or is not a math question |
| 13 | """ |
| 14 | # Edge Case: Non-math questions |
| 15 | if not question.startswith("What is"): |
| 16 | raise ValueError("syntax error") |
| 17 | |
| 18 | # Remove the "What is" prefix and the trailing question mark |
| 19 | expression = question[8:-1].strip() |
| 20 | |
| 21 | # Edge Case: Empty expression after "What is" |
| 22 | if not expression: |
| 23 | raise ValueError("syntax error") |
| 24 | |
| 25 | # Define operation mappings |
| 26 | operations = { |
| 27 | "plus": "+", |
| 28 | "minus": "-", |
| 29 | "multiplied by": "*", |
| 30 | "divided by": "/" |
| 31 | } |
| 32 | |
| 33 | # Tokenize the expression |
| 34 | tokens = [] |
| 35 | unknown_ops = [] # Track unknown operations for later processing |
| 36 | i = 0 |
| 37 | while i < len(expression): |
| 38 | # Skip whitespace |
| 39 | if expression[i].isspace(): |
| 40 | i += 1 |
| 41 | continue |
| 42 | |
| 43 | # Check for numbers (including negative numbers) |
| 44 | if expression[i].isdigit() or (expression[i] == '-' and i < len(expression) - 1 and expression[i+1].isdigit()): |
| 45 | start = i |
| 46 | if expression[i] == '-': |
| 47 | i += 1 |
| 48 | while i < len(expression) and (expression[i].isdigit() or expression[i] == '.'): |
| 49 | i += 1 |
| 50 | # Edge Case: Invalid number format (decimals not allowed per examples) |
| 51 | num_str = expression[start:i] |
| 52 | if '.' in num_str: |
| 53 | raise ValueError("syntax error") |
| 54 | tokens.append(int(num_str)) |
| 55 | continue |
| 56 | |
| 57 | # Check for operations |
| 58 | found_op = False |
| 59 | for word_op, symbol in operations.items(): |
| 60 | if expression.startswith(word_op, i): |
| 61 | tokens.append(symbol) |
| 62 | i += len(word_op) |
| 63 | found_op = True |
| 64 | break |
| 65 | |
| 66 | # Edge Case: Unknown operations |
| 67 | if not found_op: |
| 68 | # If we're at a position where we expect an operation or number but find something else |
| 69 | if not expression[i].isspace(): |
| 70 | # Extract the full word (sequence of non-space characters) |
| 71 | start = i |
| 72 | while i < len(expression) and not expression[i].isspace(): |
| 73 | i += 1 |
| 74 | word = expression[start:i] |
| 75 | # Include unknown operations as tokens to preserve syntax structure |
| 76 | tokens.append(word) |
| 77 | # Store unknown operation for later processing |
| 78 | unknown_ops.append((start, word)) |
| 79 | else: |
| 80 | i += 1 |
| 81 | |
| 82 | # Edge Case: Empty tokens |
| 83 | if not tokens: |
| 84 | raise ValueError("syntax error") |
| 85 | |
| 86 | # Validate token sequence - check for proper alternating pattern: number, operator, number, operator, ... |
| 87 | # First, check if the overall structure is valid (ignoring whether operators are known) |
| 88 | structural_valid = True |
| 89 | for i in range(len(tokens)): |
| 90 | # Even indices should be numbers |
| 91 | if i % 2 == 0: |
| 92 | if not isinstance(tokens[i], int): |
| 93 | structural_valid = False |
| 94 | break |
| 95 | # Odd indices should be operators (any string) |
| 96 | else: |
| 97 | if not isinstance(tokens[i], str): |
| 98 | structural_valid = False |
| 99 | break |
| 100 | |
| 101 | # If the structure is invalid, it's a syntax error |
| 102 | if not structural_valid: |
| 103 | raise ValueError("syntax error") |
| 104 | |
| 105 | # Edge Case: Expression ending with a known operator |
| 106 | if len(tokens) > 0 and isinstance(tokens[-1], str) and tokens[-1] in operations.values(): |
| 107 | raise ValueError("syntax error") |
| 108 | |
| 109 | # If the structure is valid, check for unknown operations |
| 110 | # If there are unknown operations in operator positions, it's an unknown operation error |
| 111 | for i in range(1, len(tokens), 2): # Only check operator positions |
| 112 | if tokens[i] not in operations.values(): |
| 113 | raise ValueError("unknown operation") |
| 114 | |
| 115 | # Evaluate left to right |
| 116 | result = tokens[0] |
| 117 | |
| 118 | # Edge Case: Division by zero |
| 119 | for i in range(1, len(tokens), 2): |
| 120 | operator = tokens[i] |
| 121 | operand = tokens[i+1] |
| 122 | |
| 123 | if operator == "+": |
| 124 | result += operand |
| 125 | elif operator == "-": |
| 126 | result -= operand |
| 127 | elif operator == "*": |
| 128 | result *= operand |
| 129 | elif operator == "/": |
| 130 | # Edge Case: Division by zero |
| 131 | if operand == 0: |
| 132 | raise ValueError("syntax error") |
| 133 | result //= operand # Integer division as per examples |
| 134 | |
| 135 | return result |
| 136 | # Handled Edge Cases: Non-math questions, Empty expression, Invalid number format, Unknown operations, Empty tokens, Expression starting/ending with operator, Non-number at even position, Non-operator at odd position, Division by zero |