Longest Substring Without Repeating Characters

Longest Substring Without Repeating Characters is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the Sliding Window pattern, in the Variable Size (Condition-Based) subpattern.

Problem statement

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

Example 1:

Input: s = "abcabcbb" Output: 3 Explanation: The answer is "abc", with the length of 3.

Example 2:

Input: s = "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1.

Example 3:

Input: s = "pwwkew" Output: 3 Explanation: The answer is "wke", with the length of 3. Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

Constraints:

- 0 <= s.length <= 5 104

- s consists of English letters, digits, symbols and spaces.

Topics and companies

Topics: Hash Table, String, Sliding Window.

Reported in interviews at Amazon, Bloomberg, Microsoft, Facebook, Apple, Adobe, eBay, Goldman Sachs, Google, Alation, VMware, Oracle and others.

How to practise Longest Substring Without Repeating Characters on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(n) time and O(1) space.

Open Longest Substring Without Repeating Characters in the code editor, or read the Longest Substring Without Repeating Characters editorial for a worked solution with its approach and complexity analysis.

Where Longest Substring Without Repeating Characters sits in the DSA pattern sheet

• Sliding Window pattern guide
• Variable Size (Condition-Based) subpattern
• The full DSA patterns sheet
• All coding practice problems

Problems related to Longest Substring Without Repeating Characters

Other problems that use the same Variable Size (Condition-Based) and Sliding Window techniques:

• Contains Duplicate II — Easy, same subpattern
• Continuous Subarrays — Medium, same subpattern
• Find Longest Special Substring That Occurs Thrice I — Medium, same subpattern
• Frequency of the Most Frequent Element — Medium, same subpattern
• Fruit Into Baskets — Medium, same subpattern
• Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit — Medium, same subpattern