Longest Substring Without Repeating Characters | Sliding Window Explained Simply

Описание: Learn how to solve Longest Substring Without Repeating Characters — one of the most common JavaScript coding interview questions — with a clear, optimized step-by-step explanation.

In this tutorial, you’ll understand both the brute force approach and the optimized sliding window technique.
By the end, you’ll know how to find the length of the longest substring with no repeating letters — efficiently and confidently!

💡 What You’ll Learn:

What the problem is really asking for

Brute force vs optimized approaches

Sliding window technique explained visually

Real-world analogy to remember the logic

Step-by-step JavaScript code walkthrough

Example walkthroughs with multiple test cases

Time and space complexity explained clearly

📘 Code Example:

function lengthOfLongestSubstring(s) {
let left = 0, maxLen = 0;
const seen = new Set();
for (let right = 0; right s.length; right++) {
while (seen.has(s[right])) {
seen.delete(s[left]);
left++;
}
seen.add(s[right]);
maxLen = Math.max(maxLen, right - left + 1);
}
return maxLen;
}


🎯 Why This Matters:
This problem helps you master one of the most powerful algorithm patterns — the sliding window technique.
Once you learn it, you’ll unlock similar problems like:

Longest substring with K distinct characters

Minimum window substring

Longest repeating substring

Permutation in string

🧠 Skill Level: Beginner to Intermediate
🕒 Time Complexity: O(n)
📚 Language Used: JavaScript

👨‍💻 Next in Series:

🧩 Two Sum Explained Simply

🔢 3Sum JavaScript Tutorial

🪟 Minimum Window Substring (Coming Soon)

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