Longest Substring Without Repeating Characters

Longest Substring Without Repeating Characters | AlgoChronicle

Step 1

Know these before you start

Tick what you already know

Concept video

Step 2

Try it on paper

5–10 minutes, no code yet

ProblemProblem statementGiven a string s, find the length of the longest substring without repeating characters.Read

Problem Statement

Given a string s, find the length of the longest substring without repeating characters.

Imported 2026-10-09 from NeetCode auto-sync (reviewed).

Input / Output

Input:  s = "abcabcbb"
Output: 3
Explanation: "abc" is the longest valid substring.

Input:  s = "pwwkew"
Output: 3

Step 6

Get it accepted

All test cases pass

Step 7

Review it so it sticks

Re-solve from memory after

Solve it yourself before you look

Reading the solution first feels like progress, but it makes the next similar problem — and the interview version — much harder, because you skipped the part where you figure it out. Give it an honest 20–30 minutes. Stuck? Re-read the pattern, watch the concept video, or try the brute force first.

Hidden: approach · solution code · optimal solution

Revising this one?

→Solve it from memory before peeking
→Say the pattern out loud, not just the code
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