File: crawler-log-folder/solution.py

Date: 2026-06-06

Time: 16:09

Purpose

This file solves LeetCode 1598: Crawler Log Folder. It simulates a filesystem crawler that starts at a main (root) folder, processes a sequence of navigation operations, and returns how many "../" operations you'd need to get back to root from wherever you end up. It's a single-class, single-method solution following the repo's standard structure.

Key Components

Solution.minOperations(logs: List[str]) -> int

The only method. Takes a list of log strings representing folder change operations and returns the minimum number of parent-directory moves to return to root.

Three operation types handled:

• "../" — move up one level (decrement depth, floored at 0)
• "./" — stay in current folder (no-op)
• Any other string (e.g. "d1/") — move into a child folder (increment depth)

The return value is simply the final depth, since each level of depth requires exactly one "../" to undo.

Patterns

Depth counter instead of stack. The problem could be modeled with an explicit path stack, but since we only need the distance from root — not the actual path — a single integer depth suffices. This is a common simplification when you need magnitude, not identity.

Clamp on decrement. max(0, depth - 1) prevents going above root, which matches real filesystem semantics where cd .. at / keeps you at /.

Dependencies

Imports: List from typing — used solely for the type annotation on logs.

Imported by: crawler-log-folder/test_solution.py — the corresponding test file. The massive "Imported By" list in the prompt is noise from the repo's shared test infrastructure importing Solution classes across problems; this solution is only meaningfully consumed by its own test file.

Flow

1. Initialize depth = 0 (at root).

2. Iterate through each log entry exactly once.

3. Branch on the string value: decrement-with-floor for "../", skip for "./", increment for anything else.

4. Return depth.

Single pass, O(n) time, O(1) space.

Invariants

• depth >= 0 at all times — enforced by max(0, depth - 1). You can never navigate above root.
• The return value equals the number of "../" operations needed, which is exactly the current depth. This works because each child-folder entry adds exactly 1 to depth, and each parent move removes exactly 1.

Error Handling

None. The method trusts that logs contains only valid operation strings ("../", "./", or "<name>/"). Invalid input (empty strings, None entries, non-string elements) would silently increment depth via the else branch — there's no validation. This is standard for LeetCode solutions where inputs are guaranteed well-formed.

Topics to Explore

• [file] crawler-log-folder/test_solution.py — See the edge cases being tested (empty logs, all "../" from root, mixed operations)
• [file] crawler-log-folder/plan.md — The approach reasoning and complexity analysis before implementation
• [general] depth-vs-stack-tradeoff — When to use a counter vs. maintaining an explicit path stack (relevant to problems like simplify-path, which needs the actual path)
• [function] valid-parentheses/solution.py:isValid — Another stack-depth problem, but one that requires the stack (not just a counter) because bracket types must match

Beliefs

• crawler-log-folder-depth-floor — minOperations guarantees depth >= 0 throughout execution; navigating above root is a no-op
• crawler-log-folder-linear — The solution is O(n) time and O(1) space with a single pass over the logs list
• crawler-log-folder-implicit-child — Any log string that isn't "../" or "./" is treated as entering a child folder with no validation of the folder name
• crawler-log-folder-depth-equals-answer — The return value is the raw depth counter, relying on the invariant that depth equals the minimum number of "../" operations to reach root