JavaScript LeetCode Problems: A Guide from Zero to Pro

JavaScript on LeetCode: Where to Start and How Not to Give Up After the Second Problem

LeetCode is not just a site with problems. For a JavaScript developer, it's a real logic trainer that turns "I know syntax" into "I can solve problems." But many beginners quit LeetCode after the first Medium problem. Why? Because JavaScript LeetCode problems require not knowledge of frameworks, but the ability to think algorithmically. In this article, I'll tell you how to approach the process systematically, which topics to learn first, and how to write code you won't be ashamed to show in an interview.

This article is written for the educational portal pythonlib.ru — here we love complex topics and clear explanations. Let's go.

Why LeetCode Specifically for JavaScript?

In the world of frontend and Node.js backend, JavaScript LeetCode problems have become the de facto standard for testing candidates. Google, Amazon, Meta — they all use similar algorithmic sections. But it's not just about interviews. By solving problems, you:

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• Learn to write clean and efficient code
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• Understand how data structures work internally
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• Develop a "feel" for algorithm complexity (Big O)
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• Stop being afraid of working with arrays, strings, and objects
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And most importantly — solving algorithms in JavaScript makes you more confident. When you can write a function in 10 minutes that processes a million records without lag, it changes your attitude towards code in general.

Where to Start: A Learning Plan for Beginners

Many try to storm Hard-level problems and quickly burn out. The best strategy is to go from simple to complex. Here is a proven plan that I recommend to students of pythonlib.ru.

Step 1. Syntax Basics (if you've just started learning JS)

Before diving into LeetCode, make sure you firmly know:

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• Data types and type coercion
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• Functions, arrow functions, closures
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• Array methods: map, filter, reduce, forEach
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• Working with objects and Map/Set
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• Spread operator and destructuring
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Without this, even a simple problem will turn into torture. For example, the "Two Sum" problem (the most popular on LeetCode) is solved in 4 lines if you know Map:

function twoSum(nums, target) {\n    const map = new Map();\n    for (let i = 0; i < nums.length; i++) {\n        const complement = target - nums[i];\n        if (map.has(complement)) {\n            return [map.get(complement), i];\n        }\n        map.set(nums[i], i);\n    }\n}\n

See? Without understanding Map, you would have used a double loop and gotten O(n²). But here — linear complexity.

Step 2. Practice "Easy" Problems by Topic

JavaScript LeetCode problems for beginners are at the Easy level. Don't chase quantity. It's better to solve 30 problems mindfully than 100 — "however they turn out." Break them down by topic:

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• Arrays (slicing, removing duplicates, rotations)
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• Strings (palindromes, anagrams, substring search)
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• Hash tables (pair search, frequency counting)
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• Linked lists (reversal, merging)
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Example of a useful problem: "Valid Anagram". A classic that teaches you to work with strings and hashes:

function isAnagram(s, t) {\n    if (s.length !== t.length) return false;\n    const count = {};\n    for (let char of s) {\n        count[char] = (count[char] || 0) + 1;\n    }\n    for (let char of t) {\n        if (!count[char]) return false;\n        count[char]--;\n    }\n    return true;\n}\n

Notice: we don't use sort() — th