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    codstak / sum-two-numbersDSA challenge
    DSA5–10 min

    Challenge 03

    Sum of two numbers

    Practice a focused algorithm problem, verify edge cases, and review the quality of your approach.

    Define the function contract
    Handle positive and negative values
    Return the result without extra output
    solution.pytests

    def sum_two_numbers(a, b):

    return a + b

    # Try a few inputs

    result = sum_two_numbers(4, 7)

    Test results

    Run the visible examples to check your solution.

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    Five ways to practice

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    20 challenges

    JavaScript

    Build instincts for runtime behavior, references, closures, promises, and async failures.

    Explore JavaScript
    20 lessons

    TypeScript

    Learn type annotations, objects, unions, and safe everyday patterns step by step.

    Explore TypeScript
    20 builds

    React

    Build interview-style interfaces with state, effects, forms, accessibility, and feedback.

    Practice React interviews
    10 API challenges

    Node.js

    Practice HTTP contracts, validation, authorization, webhooks, and resilient API behavior.

    Explore Node.js
    Problem solving

    DSA

    Strengthen your core data structures and algorithmic thinking through focused exercises.

    Explore DSA

    How it works

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    01

    Choose a focused challenge

    Work on one practical concept at a time, from data structures and runtime reasoning to types, UI behavior, and API contracts.

    02

    Build or solve it

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    03

    Build evidence as you improve

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    Codstak Coach

    Ready for this challenge

    Why does my state update show the old value?
    React schedules state updates. Instead of reading the value immediately after setting it, derive what you need during render—or use the callback form when the next value depends on the previous one.
    Give me a hint
    Ask a question
    Review my code

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    • JavaScript, TypeScript, React, Node.js, and DSA practice
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    • 1,200 AI hints over 3 months
    • Progressive hints across every practice track
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    • Solution reviews tied to the skill being practised
    • A growing picture of your demonstrated skills

    AI hints estimator

    How many hints will you use?

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    4
    1 / week15 / week
    Sometimes

    When I'm genuinely stuck

    Hints over 3 months

    144

    Free (30 over 3 mo)AI Coach (1,200 over 3 mo)

    AI Coach gives you plenty of room at this pace.

    That's 144 hints — the 3-month AI Coach plan includes 1,200.

    AI Coach early access is built around guided progression and skill evidence. It does not guarantee an interview outcome, and joining does not start a subscription or require a credit card.

    What comes next

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    JavaScript · liveTypeScript · liveReact · liveNode.js · liveDSA · live

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