Longest Contiguous Substring in Which No Character Repeats
Company: ByteDance
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Onsite
Given a string `s`, return the length of the longest contiguous substring of `s` in which no character appears more than once.
### Function Signature
```python
def longest_distinct_substring(s: str) -> int:
```
### Rules
- A substring is a contiguous run of characters of `s`. A subsequence that skips characters does not count.
- Characters are compared exactly: `'a'` and `'A'` are different, and a space or a punctuation mark is a character like any other.
- The empty string has answer `0`; any non-empty string has answer at least `1`.
### Constraints
- `0 <= len(s) <= 100000`
- Every character of `s` is printable ASCII (codes `32` through `126`).
### Examples
**Example 1**
```text
Input: s = "abcbdea"
Output: 5
```
The substring `"cbdea"` (positions `2` through `6`) has five different characters. Every longer substring contains `b` twice.
**Example 2**
```text
Input: s = "abba"
Output: 2
```
`"ab"` and `"ba"` both have length `2`, and every substring of length `3` or more repeats a character.
**Example 3**
```text
Input: s = "zzzz"
Output: 1
```
Overview: A string problem that asks for the length of the longest contiguous substring in which no character repeats. It tests telling substrings apart from subsequences, exact case-sensitive character handling, and an efficient pass over strings of up to 100,000 printable characters.
Read the full ByteDance Software Engineer interview experience this question came from
Implement `longest_distinct_substring(s)`: given a string `s`, return the length of the longest contiguous substring of `s` in which no character appears more than once.
### Rules
- A substring is a contiguous run of characters of `s`. A subsequence that skips characters does not count.
- Characters are compared exactly: `'a'` and `'A'` are different, and a space or a punctuation mark is a character like any other.
- The empty string has answer `0`; any non-empty string has answer at least `1`.
- The return value is a single integer. It can never exceed 95 (the number of printable ASCII characters), so it fits in a 32-bit `int` in every language; no value can exceed 2^31 - 1.
### Constraints
- `0 <= len(s) <= 100000`
- Every character of `s` is printable ASCII (codes `32` through `126`).
### Example 1
```text
Input: s = "abcbdea"
Output: 5
```
The substring `"cbdea"` (positions `2` through `6`) has five different characters. Every longer substring contains `b` twice.
### Example 2
```text
Input: s = "abba"
Output: 2
```
`"ab"` and `"ba"` both have length `2`, and every substring of length `3` or more repeats a character.
Constraints
- 0 <= len(s) <= 100000
- Every character of s is printable ASCII (codes 32 through 126).
Examples
Input: ('',)
Expected Output: 0
Explanation: The empty string has answer 0.
Input: ('a',)
Expected Output: 1
Explanation: A single character is a valid substring of length 1.
Hints
- Only contiguous runs of s count; a selection of characters that skips a position is not a substring.
- Compare characters exactly: an upper-case letter and its lower-case form differ, and spaces and punctuation marks are characters too.
- There are only 95 printable ASCII characters, so no qualifying substring can be longer than 95.