Longest Distinct String

Given a string s, return the length of its longest contiguous substring in which no character appears more than once.
A substring is a contiguous sequence of characters within s. Return only the maximum length, not the substring itself.

Function
longestDistinctString(s: String) → int

Examples
Example 1
s = "abcc"
return = 3
The substring "abc" contains no repeated character and has length 3.
Example 2
s = "abcabcbb"
return = 3
Substrings such as "abc" have length 3, and every longer substring repeats a character.
Example 3
s = "bbbbb"
return = 1
Every distinct-character substring contains only one b.

Constraints
1 <= s.length <= 100000
s contains printable ASCII characters.

The trick is a sliding window with a hash map from character to last seen index. Walk right pointer i across the string. If s[i] was seen at an index at or after left, jump left to that index plus one. Then record the window length i - left + 1 and update the best. That's O(n) time and O(1) extra space, since printable ASCII caps the map at 128 or so entries. The common pitfall is moving left backward. If a character was seen before the current window, you must ignore it, so take the max of left and last+1. Another slip is returning the substring when the task wants only the length. Constraints go up to 100000, so brute force over all substrings will time out. If you freeze on the pointer logic, StealthCoder is the hedge during the live OA, giving you the working template fast.

If you see this problem in your OA tomorrow, the play is to recognize the pattern in 30 seconds. StealthCoder buys you that recognition.