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

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This question is commonly asked for Software Engineer candidates at Antra during technical interviews.

Longest Substring Without Repeating Characters

Quick Overview

This question tests a software engineer's ability to apply sliding window techniques and string manipulation to optimize character uniqueness tracking. It is a classic coding problem that evaluates practical algorithm design, commonly used to assess proficiency with hash-based data structures and efficient string traversal in technical interviews.

Company: Antra

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Technical Screen

## Longest Substring Without Repeating Characters Given a string `s`, find the length of the **longest substring** that contains no repeating characters. A substring is a contiguous, non-empty sequence of characters within the string. The string may contain any printable ASCII characters, including letters, digits, symbols, and spaces. ### Examples Example 1: - Input: `s = "abcabcbb"` - Output: `3` - Explanation: The longest substring without repeating characters is `"abc"`, which has length 3. Example 2: - Input: `s = "bbbbb"` - Output: `1` - Explanation: The longest substring without repeating characters is `"b"`, with length 1. Example 3: - Input: `s = "pwwkew"` - Output: `3` - Explanation: The longest substring without repeating characters is `"wke"`, with length 3. Note that `"pwke"` is a subsequence, not a substring. Example 4: - Input: `s = ""` - Output: `0` - Explanation: The empty string has no substring, so the answer is 0. ### Constraints - `0 <= s.length <= 5 * 10^4` - `s` consists of printable ASCII characters (`' '` through `'~'`, i.e. character codes 32 through 126). ### Required Function Implement a function that takes the string `s` and returns an integer: the length of the longest substring of `s` with all distinct characters.

Quick Answer: This question tests a software engineer's ability to apply sliding window techniques and string manipulation to optimize character uniqueness tracking. It is a classic coding problem that evaluates practical algorithm design, commonly used to assess proficiency with hash-based data structures and efficient string traversal in technical interviews.

Given a string `s`, find the length of the **longest substring** that contains no repeating characters. A substring is a contiguous, non-empty sequence of characters within the string. The string may contain any printable ASCII characters, including letters, digits, symbols, and spaces. ### Examples Example 1: - Input: `s = "abcabcbb"` - Output: `3` - Explanation: The longest substring without repeating characters is `"abc"`, which has length 3. Example 2: - Input: `s = "bbbbb"` - Output: `1` - Explanation: The longest substring without repeating characters is `"b"`, with length 1. Example 3: - Input: `s = "pwwkew"` - Output: `3` - Explanation: The longest substring without repeating characters is `"wke"`, with length 3. Note that `"pwke"` is a subsequence, not a substring. Example 4: - Input: `s = ""` - Output: `0` - Explanation: The empty string has no substring, so the answer is 0. ### Constraints - `0 <= s.length <= 5 * 10^4` - `s` consists of printable ASCII characters (`' '` through `'~'`, i.e. character codes 32 through 126). ### Required Function Implement a function that takes the string `s` and returns an integer: the length of the longest substring of `s` with all distinct characters.

Constraints

0 <= s.length <= 5 * 10^4
s consists of printable ASCII characters (codes 32 through 126)

Examples

Input: ("abcabcbb",)

Expected Output: 3

Explanation: The longest distinct substring is "abc" (length 3).

Input: ("bbbbb",)

Expected Output: 1

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

Input: ("pwwkew",)

Expected Output: 3

Explanation: "wke" is the longest substring with no repeats (length 3).

Input: ("",)

Expected Output: 0

Explanation: An empty string has no substring, so the answer is 0.

Input: ("a",)

Expected Output: 1

Explanation: A single character is trivially distinct (length 1).

Input: ("abcdef",)

Expected Output: 6

Explanation: All characters are distinct, so the whole string qualifies (length 6).

Input: ("dvdf",)

Expected Output: 3

Explanation: The repeat 'd' is not at the window's left edge; the best window is "vdf" (length 3).

Input: ("tmmzuxt",)

Expected Output: 5

Explanation: After skipping past the duplicate 'm', the window "mzuxt" gives length 5.

Input: (" ",)

Expected Output: 1

Explanation: A single space is a valid one-character substring (length 1).

Input: ("abba",)

Expected Output: 2

Explanation: When the second 'a' appears, the window start must jump forward; the best is "ab" or "ba" (length 2).

Input: ("a!a!b@b@c#",)

Expected Output: 4

Explanation: Mixed letters and symbols; the longest distinct window is "b@c#" (length 4).

Hints

Use a sliding window with two pointers. Expand the right edge one character at a time and shrink the left edge whenever a character repeats.
Track the most recent index at which each character was seen. When you encounter a repeat that lies inside the current window, jump the window start to just past that previous occurrence.
The answer is the maximum window width (right - left + 1) observed while scanning. This runs in O(n) time because each character is visited once.

Quick Overview