File: final-value-of-variable-after-performing-operations/solution.py

Date: 2026-06-06

Time: 16:32

final-value-of-variable-after-performing-operations/solution.py

Purpose

This file solves LeetCode 2011: Final Value of Variable After Performing Operations. It provides the single exported function max_value that computes the result of applying a sequence of increment/decrement operations to a variable starting at zero.

Key Components

max_value(operations: list[str]) -> int — The sole function. Takes a list of operation strings (each one of "++X", "X++", "--X", "X--") and returns the final integer value after applying them all sequentially, starting from 0.

Patterns

The implementation exploits a structural invariant of the input: all four valid operation strings share the property that the second character (index 1) determines the operation. "++X" and "X++" both have "+" at index 1; "--X" and "X--" both have "-" at index 1. This lets the function avoid string matching or parsing — it just checks op[1].

This is a common LeetCode idiom: finding a positional character that discriminates all cases, trading readability for brevity.

Dependencies

Imports: None. Pure function with no external dependencies.

Imported by: The "Imported By" list in the prompt is misleading — it lists hundreds of unrelated test files. The actual consumer is final-value-of-variable-after-performing-operations/test_solution.py. The other test files likely appear due to a project-wide import scanning tool that picks up transitive or structural matches.

Flow

1. Initialize x = 0.

2. Iterate over each operation string in operations.

3. Inspect op[1] — if "+", increment x; otherwise, decrement.

4. Return x.

The entire function is a single linear pass — O(n) time, O(1) space.

Invariants

• Input contract: Every string in operations must be one of the four valid forms. The function does not validate this — any string with "+" at index 1 increments, anything else decrements.
• Starting value: x always starts at 0, matching the problem specification.
• Return value: Always an integer in the range [-len(operations), len(operations)].

Error Handling

None. If operations contains strings shorter than 2 characters, op[1] will raise an IndexError. If operations is empty, the function correctly returns 0 (the loop body never executes).