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What difficulty level is this coding question?

This is a Medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Amazon.

What role is this question designed for?

This question is commonly asked for Data Scientist candidates at Amazon during technical interviews.

Determine Length of Longest Unique Substring

Quick Overview

This question evaluates string-processing skills and algorithmic problem-solving, including handling character uniqueness and performance considerations. Commonly asked in Coding & Algorithms interviews to assess a candidate's ability to implement efficient solutions and reason about time/space trade-offs, it targets practical application rather than purely conceptual understanding.

Company: Amazon

Role: Data Scientist

Category: Coding & Algorithms

Difficulty: Medium

Interview Round: Technical Screen

##### Scenario Online assessment: coding portion that follows the SQL questions. ##### Question Implement a function that, given a string s, returns the length of the longest substring without repeating characters. ##### Hints Use a sliding window and a hash map to track the latest index of each character.

Quick Answer: This question evaluates string-processing skills and algorithmic problem-solving, including handling character uniqueness and performance considerations. Commonly asked in Coding & Algorithms interviews to assess a candidate's ability to implement efficient solutions and reason about time/space trade-offs, it targets practical application rather than purely conceptual understanding.

Given a string `s`, return the length of the longest substring of `s` that contains no repeating characters. A substring is a contiguous sequence of characters within the string. The substring must not contain any character more than once. **Examples** - `s = "abcabcbb"` -> `3` (the answer is `"abc"`, length 3). - `s = "bbbbb"` -> `1` (the answer is `"b"`, length 1). - `s = "pwwkew"` -> `3` (the answer is `"wke"`, length 3; note `"pwke"` is a subsequence, not a substring). - `s = ""` -> `0`. Return the integer length of the longest such substring.

Constraints

0 <= len(s) <= 5 * 10^4
s consists of English letters, digits, symbols, and spaces.
The empty string returns 0.

Examples

Input: ("abcabcbb",)

Expected Output: 3

Explanation: The longest substring without repeats is "abc", length 3.

Input: ("bbbbb",)

Expected Output: 1

Explanation: Every character is the same, so the best is a single "b".

Input: ("pwwkew",)

Expected Output: 3

Explanation: "wke" has length 3; "pwke" is a subsequence, not a substring.

Input: ("",)

Expected Output: 0

Explanation: An empty string has no characters, so the length is 0.

Input: ("a",)

Expected Output: 1

Explanation: A single character is trivially unique.

Input: ("dvdf",)

Expected Output: 3

Explanation: The window jumps past the first 'd' to give "vdf", length 3.

Input: ("abba",)

Expected Output: 2

Explanation: After reaching the second 'a', start must not move backward; "ab" and "ba" each give length 2.

Input: (" ",)

Expected Output: 1

Explanation: A single space counts as a character, length 1.

Input: ("tmmzuxt",)

Expected Output: 5

Explanation: "mzuxt" is the longest unique window, length 5.

Input: ("abcdefg",)

Expected Output: 7

Explanation: All characters distinct, so the whole string qualifies.

Hints

Use a sliding window: keep a left pointer `start` and scan with a right pointer.
Store the most recent index of each character in a hash map.
When you see a character already inside the current window (its last index >= start), jump `start` to just past that previous occurrence instead of shrinking one step at a time.
Track the maximum window length (right - start + 1) as you go.

Quick Overview