Find the Longest Substring without Repeated Characters
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
Given a string, find the maximum length of a contiguous substring containing no repeated character.
### Constraints and Clarifications
Use a length-only return value as the practice interface, so tied longest substrings need no tie-breaking rule. Treat the input as a sequence of characters with exact equality and no normalization; no encoding or numerical size bounds were reported. The empty string returns zero.
### Example
For "abcaef", the longest valid substring is "bcaef", so the length is 5.
### What a Strong Answer Covers
Maintain a valid sliding window, advance its left boundary only when necessary, and avoid moving it backward when a character was last seen before the current window.
### Follow-up Questions
- Why is max(left,last_seen+1) needed in a last-position implementation?
- How would you return a substring as well as its length after defining a tie rule?
Overview: Find the longest nonrepeating substring with a sliding window and last-seen positions. Prove why the left boundary must never move backward and account for empty input and character representation.
Given a string, return the maximum length of a contiguous substring containing no repeated character. Implement longestUniqueSubstringLength(text). Compare characters exactly and do not normalize them. Return only the length, so tied longest substrings need no tie rule. The empty string returns zero.
Constraints
- text is a string of characters; the source gives no length bound or encoding restriction.
- A substring is contiguous and each of its characters must be distinct.
- Equality is exact and no normalization is applied.
- Return 0 for the empty string.
Examples
Input: ('',)
Expected Output: 0
Explanation: There is no nonempty substring.
Input: ('a',)
Expected Output: 1
Explanation: The one character is distinct.
Hints
- A substring with no repeated character may start or end anywhere in the text.
- The result is a length, so equal-length substrings produce the same answer.