ProgrammersOS Challenges
Test your knowledge. Sharpen your coding skills. Predict outputs, debug errors, and review code in seconds.
Fill in Array Transformation Method
Fill in the missing array method to double every number in the list.
Quick Skill Boosters
Incrementing Number & Postfix Operation
What will this JavaScript code output to the console?
Python List Slicing Step
What is the output of this Python slicing expression?
Fix Const Reassignment Error
This code throws a TypeError because it reassigns a const variable. Fix the declaration keyword.
Fill in Array Transformation Method
Fill in the missing array method to double every number in the list.
Off-By-One Sum Loop Boundary
The function sum_to_n(5) should return 15 (1+2+3+4+5), but it currently returns 10. Find the bug in the range boundary.
Legacy JavaScript Code Smells
Select all anti-patterns or code quality issues present in this legacy helper function.
Sequential Initialization & Logging
Arrange the four statements into the correct execution sequence to declare variables, compute the sum, and print the result.
Mutable Default Argument Trap in Python
Which line contains the subtle mutable default argument bug that persists state between function calls?
Array Deduplication: Set vs Filter
Which code snippet demonstrates the most idiomatic, modern, and high-performance approach to removing duplicate values from an array in JavaScript?
Strict vs Loose Inequality Boundary
Compare Version A and Version B. What is the difference when `age = 18`?
JavaScript Microtask vs Macrotask Event Loop
What is the exact order of console logs when this script executes in the JavaScript event loop?
Hash Map Average Lookup Complexity
What is the average time complexity of searching for a key in a Hash Map with a uniform hash function?
JavaScript NaN Self-Equality
In JavaScript, does the expression `NaN === NaN` evaluate to true?
ACID Database Properties
Which of the following are valid properties in the database ACID acronym? (Select all that apply)
High-Concurrency ID Lookup
You are building an in-memory service that searches through 500,000 active user records. Which data structure generally provides the fastest key-based retrieval when keyed by integer ID?
OOP Pillars Matching
Match each Object-Oriented Programming pillar with its core principle.
Networking Protocol Ports
Match each internet protocol with its standard default port number.
Sudden Flash Traffic Spike
Your web application experiences a sudden 10x traffic surge causing database CPU to reach 99%. Which architectural change will most immediately alleviate database load?
Idempotent HTTP Methods
Which of the following HTTP methods are defined as idempotent according to REST standards?
React State Immutability
Which statement about React state updates is strictly correct?
Standard Git Feature Branch Workflow
Arrange the standard Git commands in order to create a feature branch, commit changes, and push upstream.
Data Structure Characteristics
Match each data structure with its primary operational characteristic.
Binary Search Iteration Sequence
What is the missing step in the standard Binary Search loop?
Trace Accumulator Loop State
Trace the evolution of variable total through each iteration of the loop. What is the final value printed?
Synchronous Call Stack Sequence
In what sequence will the letters be logged to the console?
Identify Algorithmic Pattern
Which algorithmic paradigm is characterized by solving subproblems, caching their results (memoization), and building up optimal solutions?
Identify Runtime Error Type
What type of error will JavaScript throw when executing `null.toUpperCase()`?
JavaScript Operators Quick Check
What does `typeof null` return in JavaScript due to a historical quirk?
Python Bool Evaluation Speed Test
What does `bool([])` evaluate to in Python?
Featured Daily: Closure Variable Retention
What will this closure counter function return on its second call?
Stack Balance Verification Logic
When parsing opening brackets '(' and '{', which operation is performed on the stack?
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