Evaluate Dependent Variable Assignments

Evaluate Dependent Variable Assignments

You are building a lightweight configuration evaluator for an autonomous simulation engine. You are given a list of assignment statements. Each statement assigns an integer value or an arithmetic expression to a unique variable name.

Crucially, expressions may reference variables defined later in the input list. If all references are valid and contain no circular dependencies, evaluate the integer value of every variable.

Requirements

Each statement is a string formatted as: " = "

• `` is an alphanumeric identifier (e.g., "x", "steer_gain").
• `` contains non-negative integer literals, variable identifiers, and the binary operators +, -, and *. Parentheses ( and ) may be present.
• Whitespace around tokens should be ignored.
• If there is a circular dependency (e.g., a = b + 1 and b = a * 2) or an undefined variable reference, return an empty list [].
• Otherwise, return a list of tuples (var_name, evaluated_value) in the exact order the variables were introduced in the input.

Function Signature

def evaluate_assignments(statements: list[str]) -> list[tuple[str, int]]:
    pass

Constraints

• 1 <= len(statements) <= 2,000
• Each variable identifier consists of 1 to 30 ASCII alphanumeric characters and underscores.
• No variable is defined more than once on the left-hand side.
• Expressions contain at most 50 tokens.
• Dependency chains can be up to 2,000 variables deep.
• Values fit within standard 64-bit signed integers (or arbitrary-precision integers in Python).
• Division by zero is not tested (only +, -, * are supported).

Examples

Example 1:

statements = [
    "speed = base_speed * 2",
    "accel = 5",
    "base_speed = accel + 10"
]
# base_speed = 5 + 10 = 15
# speed = 15 * 2 = 30
# accel = 5

output = evaluate_assignments(statements)
# Output: [("speed", 30), ("accel", 5), ("base_speed", 15)]

Example 2:

statements = [
    "x = y + 1",
    "y = x * 2"
]

output = evaluate_assignments(statements)
# Output: [] (circular dependency detected)

Example 3:

statements = [
    "a = b + 3",
    "c = 10"
]

output = evaluate_assignments(statements)
# Output: [] (variable 'b' is never defined)