Find the Second-Greatest Distinct Digit
Company: Meta
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: easy
Interview Round: Other
### Problem
The string `s` contains lowercase letters and decimal digits. Return the second-greatest distinct digit value occurring in it, or `-1` when fewer than two different digits occur.
```cpp
class Solution {
public:
int secondHighest(string s);
};
```
### Examples
**Example 1:**
```text
s = "x90889y"
Output: 8
Explanation: Distinct digits are 0, 8, and 9.
```
**Example 2:**
```text
s = "a000b"
Output: -1
Explanation: Repeated zero is still only one distinct digit.
```
### Constraints
- `1 <= s.length <= 500`.
- Every character is a lowercase English letter or a digit.
### Clarifying Questions
Repeated copies of the largest digit do not create a second-largest distinct value. Return an integer digit, not its character code.
```hint Inspect the structure
How do repeated digits, letters, and zero affect the meaning of second-greatest distinct digit?
```
### Reasoning checkpoints
- Exclude letters and repeated occurrences when ranking distinct digit values.
- Handle zero as a valid digit and distinguish it from the missing-result sentinel.
### Optional extensions
How could two running maxima replace the presence table?
Overview: Find the Second-Greatest Distinct Digit. The string s contains lowercase letters and decimal digits. Return the second-greatest distinct digit value occurring in it, or -1 when fewer than two different digits occur.