Longest Substring Without Repeating Characters

MediumSliding Window

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Problem

Given a string s, find the length of the longest substring that does not contain any repeating characters.

Examples

Example 1

Input:s = "abcabcbb"

Output:3

The answer is "abc".

Example 2

Input:s = "bbbbb"

Output:1

Constraints

0 <= s.length <= 5 * 10^4

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How to approach it: the Sliding Window pattern

A window — a contiguous subarray or substring — expands and shrinks as it moves across the input, so you track a running condition instead of recomputing it from scratch for every possible window.

Look for this pattern when

The problem asks for the longest/shortest/best contiguous subarray or substring meeting a condition.
Brute force would recompute a sum or count for every possible window — a sign that work can be shared between overlapping ranges.

Read the full Sliding Window guide →

Video walkthroughs

Original problem on LeetCode ↗