Measure the Longest Substring Advancing One Alphabet Letter at a Time
Company: IBM
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Other
### Problem
An alphabetical continuous substring is a contiguous piece of the ordinary alphabet abcdefghijklmnopqrstuvwxyz. In lowercase `s`, return the greatest length of a substring whose next letter is always exactly one alphabet position later.
```cpp
class Solution {
public:
int longestContinuousSubstring(string s);
};
```
### Examples
**Example 1:**
```text
Input: s = "xyza"
Output: 3
Explanation: xyz is valid, but the alphabet does not wrap from z to a.
```
**Example 2:**
```text
Input: s = "ace"
Output: 1
Explanation: Every neighboring pair skips a letter, so only singleton substrings qualify.
```
### Constraints
- `1 <= s.length <= 100000`.
- s contains lowercase English letters.
### Clarifying Questions
- Can letters be skipped? No; the result must be a substring of `s`.
- Does `z` continue to `a`? No.
- Can a single letter qualify? Yes.
- Can equal adjacent letters belong to one valid run? No; each next letter must advance exactly one position.
```hint Check the boundary
Check `"za"` and `"aa"` against the exact next-letter rule.
```
Overview: Find the longest contiguous run of lowercase letters that advances exactly one alphabet position at each step without wrapping.