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@vikahaze vikahaze commented Dec 10, 2025

Problem 3577: Count the Number of Computer Unlocking Permutations

Status: ✅ Accepted (833/833 test cases passed)

Approach:

  • Verified that all computers i > 0 have complexity[i] > complexity[0]
  • If constraint satisfied, result is (n-1)! since remaining computers can be arranged arbitrarily
  • Used modulo arithmetic for large numbers

Note: Solutions for problems 3769, 3753, 3743, 3739, 3734, 3733, 3729, 2728, 3668, 3637, 3633, 3606, 3591, 3582, 3536 are written but need submission testing (LeetCode session expired). Will create separate PRs once solutions are accepted.

Summary by Sourcery

Add a validated counting solution and written explanation for problem 3577: Count the Number of Computer Unlocking Permutations.

New Features:

  • Introduce a linear-time solution for counting valid unlocking permutations based on a complexity constraint.
  • Add an English explanation document detailing the reasoning, constraints, and walkthrough for problem 3577.

Enhancements:

  • Simplify the core condition for validity by directly enforcing that all non-root computers have strictly greater complexity than computer 0.

Summary by CodeRabbit

  • New Features
    • Added a new problem with comprehensive explanation covering strategy, constraints, approach, and worked examples
    • Included complete solution implementation with optimized logic
    • Updated problem collection lists to reflect new problem addition and reorganize content

✏️ Tip: You can customize this high-level summary in your review settings.

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sourcery-ai bot commented Dec 10, 2025

Reviewer's Guide

Implements the accepted solution for problem 3577 by tightening the validity condition on complexities and adding a detailed English explanation document describing the O(n) factorial-based counting logic.

Class diagram for Solution.countPermutations implementation

classDiagram
    class Solution {
        +countPermutations(complexity: list[int]) int
    }
Loading

File-Level Changes

Change Details Files
Tighten the unlocking validity condition and compute (n-1)! under modulo when valid.
  • Use built-in list[int] type annotation instead of importing List from typing.
  • Replace the previous unique-minimum check with a stricter condition that every complexity[i] for i > 0 must be greater than complexity[0].
  • Return 0 early if any complexity[i] <= complexity[0] is found.
  • Iterate i from 1 to n-1, multiplying into an accumulator to compute (n-1)! modulo 1e9+7.
solutions/3577/01.py
Add a written explanation for problem 3577 describing the reasoning and algorithm.
  • Document input constraints, time and space complexity, and the core unlocking rule based on complexities.
  • Explain why verifying complexity[i] > complexity[0] for all i > 0 is sufficient for validity.
  • Contrast the factorial-based counting approach with a brute-force permutation enumeration.
  • Provide a step-by-step walkthrough example showing the loop, checks, and factorial accumulation.
explanations/3577/en.md

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coderabbitai bot commented Dec 10, 2025

Walkthrough

Added a new problem (3577) with explanation and Python solution, updating the type annotation from List[int] to list[int] and revising the validation logic. Updated data/book-sets.json to include the new problem ID in the All and Visualization problem sets while reorganizing adjacent ID sequences.

Changes

Cohort / File(s) Summary
Problem 3577 Addition
explanations/3577/en.md, solutions/3577/01.py
Added new explanation file detailing strategy, constraints, and step-by-step reasoning for counting valid computer unlock permutations. Added Python solution with updated type annotation (list[int]) and simplified validation logic that checks if all complexity[i] for i > 0 strictly exceed complexity[0].
Configuration Updates
data/book-sets.json
Updated All and Visualization problem ID lists: added ID 3577 to All problems, removed 3604 and 3605, and reorganized ID ranges in both sets (3561–3564, 3566–3576, 3578–3589, etc.) while maintaining the trailing endpoint at 3799.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

  • Verify logic correctness: Ensure the simplified validation condition (all complexity[i] > complexity[0]) is mathematically sound for the problem requirements
  • Cross-reference explanation and solution: Confirm the explanation file accurately describes the solution algorithm and reasoning
  • ID ordering in book-sets.json: Spot-check that the reorganized ID sequences are correct and don't skip unintended problems

Poem

🐰 Problem 3577 joins the warren's tome,
With explanations clear and code at home,
The list types shine where List once stood,
Book-sets reorder, as they should! 📚✨

Pre-merge checks and finishing touches

❌ Failed checks (1 warning)
Check name Status Explanation Resolution
Docstring Coverage ⚠️ Warning Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. You can run @coderabbitai generate docstrings to improve docstring coverage.
✅ Passed checks (2 passed)
Check name Status Explanation
Description Check ✅ Passed Check skipped - CodeRabbit’s high-level summary is enabled.
Title check ✅ Passed The title clearly and specifically summarizes the main change: adding a solution and explanation for LeetCode problem 3577 about counting computer unlocking permutations.
✨ Finishing touches
  • 📝 Generate docstrings
🧪 Generate unit tests (beta)
  • Create PR with unit tests
  • Post copyable unit tests in a comment
  • Commit unit tests in branch problems-3577-3769-3753-3743-3739-3734-3733-3729-2728-3668-3637-3633-3606-3591-3582-3536

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Hey there - I've reviewed your changes and they look great!


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Help me be more useful! Please click 👍 or 👎 on each comment and I'll use the feedback to improve your reviews.

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Actionable comments posted: 2

📜 Review details

Configuration used: CodeRabbit UI

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between 670faf3 and 93a2745.

📒 Files selected for processing (3)
  • data/book-sets.json (2 hunks)
  • explanations/3577/en.md (1 hunks)
  • solutions/3577/01.py (1 hunks)
🧰 Additional context used
🧬 Code graph analysis (1)
solutions/3577/01.py (1)
visualizations/3623/01.jsx (1)
  • MOD (39-39)
🪛 LanguageTool
explanations/3577/en.md

[style] ~57-~57: Using many exclamation marks might seem excessive (in this case: 7 exclamation marks for a text that’s 2668 characters long)
Context: ...resbyi` (since we're computing (n-1)!, and i ranges from 1 to n-1). **2.5 Re...

(EN_EXCESSIVE_EXCLAMATION)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (1)
  • GitHub Check: Sourcery review
🔇 Additional comments (3)
data/book-sets.json (1)

64-66: LGTM! Problem 3577 correctly added to the problem sets.

The problem ID is properly placed in numerical sequence within the "All" problems list.

solutions/3577/01.py (1)

6-14: LGTM! Algorithm correctly implements the permutation counting logic.

The solution efficiently validates that all computers can be unlocked (complexity[i] > complexity[0] for all i > 0) and computes (n-1)! modulo 10^9+7 when valid. The incremental factorial calculation with modulo arithmetic is correct and prevents integer overflow.

explanations/3577/en.md (1)

1-61: Excellent explanation with clear strategy and walkthrough.

The documentation provides a comprehensive breakdown of the problem-solving approach, including:

  • Complexity analysis
  • Comparison of brute force vs. optimized strategy
  • Step-by-step trace with a helpful table
  • Clear reasoning for why (n-1)! is the answer

This will be very helpful for understanding the solution.


The goal is to count valid permutations where computers can be unlocked in order. Computer 0 is already unlocked. Each computer i > 0 can only be unlocked using a previously unlocked computer j where j < i and complexity[j] < complexity[i]. Since computer 0 is the root, all other computers must be unlockable using computer 0, which means they must all have complexity greater than computer 0.

![Visualization showing computer 0 as root with arrows to other computers that must have higher complexity]
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⚠️ Potential issue | 🟡 Minor

Missing visualization image.

The markdown references an image that doesn't exist in the repository:

![Visualization showing computer 0 as root with arrows to other computers that must have higher complexity]

Either provide the image file or remove this line if the visualization isn't available yet.

Do you want me to generate sample code or suggestions for creating this visualization diagram?

🤖 Prompt for AI Agents
In explanations/3577/en.md around line 16 the markdown references a non-existent
image: the line "![Visualization showing computer 0 as root with arrows to other
computers that must have higher complexity]". Fix by either (A) adding the
missing image file to the repo at a relative path and updating the markdown to
point to that path (ensure the filename and extension match exactly and commit
the image), or (B) remove the image reference line if the visualization is not
available yet; if you add an image, keep a clear descriptive filename (e.g.,
explanations/3577/visualization.png) and commit it with the markdown change so
the link resolves.


class Solution:
def countPermutations(self, complexity: List[int]) -> int:
def countPermutations(self, complexity: list[int]) -> int:
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⚠️ Potential issue | 🟠 Major

🧩 Analysis chain

🏁 Script executed:

#!/bin/bash
# Check Python version requirements in the repository

# Look for Python version specifications
echo "=== Checking pyproject.toml ==="
fd -t f '^pyproject.toml$' -x cat {}

echo -e "\n=== Checking setup.py ==="
fd -t f '^setup.py$' -x cat {}

echo -e "\n=== Checking .python-version ==="
fd -t f '^\.python-version$' -x cat {}

echo -e "\n=== Checking other Python files for type hint style ==="
rg -t py "from typing import List" -C 2

Repository: romankurnovskii/leetcode-apps

Length of output: 11914


Use List[int] from typing module for consistency with codebase.

The type hint list[int] (PEP 585) requires Python 3.9+. The entire codebase consistently uses from typing import List with List[int] syntax. Update this method to follow the established pattern:

from typing import List

def countPermutations(self, complexity: List[int]) -> int:
🤖 Prompt for AI Agents
In solutions/3577/01.py around line 2, the method signature uses the PEP 585
form `list[int]`; change it to use the codebase-consistent typing import by
adding `from typing import List` (if not already present) and update the
signature to `def countPermutations(self, complexity: List[int]) -> int:` so the
parameter type uses `List[int]`.

@romankurnovskii romankurnovskii merged commit 3eaf78b into main Dec 10, 2025
3 checks passed
@romankurnovskii romankurnovskii deleted the problems-3577-3769-3753-3743-3739-3734-3733-3729-2728-3668-3637-3633-3606-3591-3582-3536 branch December 10, 2025 11:21
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